IDM : NeuroScience References / Further Reading

1Department of Radiology2Department of Neurology and3Department of Psychiatry4Center for Functional Neuroimaging, University of Pennsylvania, Philadelphia, PA5Harold and Margaret Milliken Hatch Laboratory of Neuroendocrinology, The Rockefeller University, New York, NY, USA

Gender is an important biological determinant of vulnerability to psychosocial stress. We used perfusion based functional magnetic resonance imaging (fMRI) to measure cerebral blood flow (CBF) responses to mild to moderate stress in 32 healthy people (16 males and 16 females). Psychological stress was elicited using mental arithmetic tasks under varying pressure. Stress in men was associated with CBF increase in the right prefrontal cortex (RPFC) and CBF reduction in the left orbitofrontal cortex (LOrF), a robust response that persisted beyond the stress task period. In contrast, stress in women primarily activated the limbic system, including the ventral striatum, putamen, insula and cingulate cortex. The asymmetric prefrontal activity in males was associated with a physiological index of stress responses—salivary cortisol, whereas the female limbic activation showed a lower degree of correlations with cortisol. Conjunction analyses indicated only a small degree of overlap between the stress networks in men and women at the threshold level of P < 0.01. Increased overlap of stress networks between the two genders was revealed when the threshold for conjunction analyses was relaxed to P < 0.05. Further, machine classification was used to differentiate the central stress responses between the two genders with over 94% accuracy. Our study may represent an initial step in uncovering the neurobiological basis underlying the contrasting health consequences of psychosocial stress in men and women.

Keywords: cerebral blood flow (CBF); arterial spin labeling (ASL); right prefrontal cortex (RPFC); left orbitofrontal cortex (LOrF); anterior cingulate cortex (ACC)

Research Articles

Prefrontal Regions Orchestrate Suppression of Emotional Memories via a Two-Phase Process

Brendan E. Depue,1,2* Tim Curran,1,2,3 Marie T. Banich1,2,3,4

Whether memories can be suppressed has been a controversial issue in psychology and cognitive neuroscience for decades. We found evidence that emotional memories are suppressed via two time-differentiated neural mechanisms: (i) an initial suppression by the right inferior frontal gyrus over regions supporting sensory components of the memory representation (visual cortex, thalamus), followed by (ii) right medial frontal gyrus control over regions supporting multimodal and emotional components of the memory representation (hippocampus, amygdala), both of which are influenced by fronto-polar regions. These results indicate that memory suppression does occur and, at least in nonpsychiatric populations, is under the control of prefrontal regions.

1 Department of Psychology, University of Colorado, Boulder, CO 80309, USA.
2 Center for Neuroscience, University of Colorado, Boulder, CO 80309, USA.
3 Institute of Cognitive Science, University of Colorado, Boulder, CO 80309, USA.
4 Department of Psychiatry, University of Denver Health Sciences, Denver, CO 80208, USA.

Visual Cognition
Issue: Volume 12, Number 5 / July 2005
Pages: 720 - 736
URL: Linking Options
Unconscious and conscious priming by forms and their parts

Bruno G. Breitmeyer , Haluk Ogmen , Jose Ramon , Jian Chen

A1 University of Houston, TX, USA

Abstract:

Using metacontrast masking techniques, in two experiments we compare unconscious and conscious response priming by targets consisting of either whole forms or else their parts. In Experiment 1 we investigate the contribution of whole forms and their figural primitives, viz., edges and corners, to the unconscious priming effect. As expected, choice RTs were fast when the invisible target and visible mask shape pairings were congruent and slower when they were incongruent. This trend, while strongest for whole-targets, also held for the target primes composed only of corners but did not hold for target primes composed only of sides. Experiment 2 showed, replicating the results of Experiment 1, that while invisible corner targets produced weaker priming effects than invisible whole targets, paradoxically visible corner target produced stronger priming effects than visible whole targets. Taken together the results of the two experiments indicate (a) that unconscious target representations and, thus, unconscious priming effects are strongest when the target is a complete rather than a partial configuration, (b) that conjunctions of line or edge orientations forming corners produce stronger unconscious target representations and priming effects than do unconscious target representations formed from nonconjoined edge or line primitives, (c) that metacontrast masking of form occurs at or beyond levels of visual processing at which feature integration of visual form primitives occurs, and (d) that, when consciously perceived, partial forms can act as stronger primes than whole forms.

Multisensory spatial interactions: a window onto functional integration in the human brain

Emiliano Macalusoa, and Jon Driverb

aNeuroimaging Laboratory, Fondazione Santa Lucia, IRCCS, Via Ardeatina, 306-00179 Rome, Italy
bInstitute of Cognitive Neuroscience and Department of Psychology, University College London, 17 Queen Square, London WC1N 3AR, UK

Available online 1 April 2005.

Incoming signals from different sensory modalities are initially processed in separate brain regions. But because these different signals can arise from common events or objects in the external world, integration between them can be useful. Such integration is subject to spatial and temporal constraints, presumably because a common source is more likely for information arising from around the same place and time. This review focuses on recent neuroimaging data concerning spatial aspects of multisensory integration in the human brain. These findings indicate not only that multisensory integration involves anatomical convergence from sensory-specific (‘unimodal’) cortices into multisensory (‘heteromodal’) brain areas, but also that multisensory spatial interactions can affect even so-called ‘unimodal’ brain regions. Such findings call for a revision of traditional assumptions about multisensory processing in the brain.

Trends in Neurosciences
Volume 28, Issue 5 , May 2005, Pages 264-271

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Proc Natl Acad Sci U S A. 2004 Dec 7;101(49):17288-93. Epub 2004 Dec 7.

Neural synchrony indexes disordered perception and cognition in schizophrenia.

Spencer KM, Nestor PG, Perlmutter R, Niznikiewicz MA, Klump MC, Frumin M, Shenton ME, McCarley RW.

Department of Psychiatry, Veterans Affairs Boston Healthcare System, Harvard Medical School, Psychiatry 116A, 940 Belmont Street, Brockton, MA 02301, USA.

Current views of schizophrenia suggest that it results from abnormalities in neural circuitry, but empirical evidence in the millisecond range of neural activity has been difficult to obtain. In pursuit of relevant evidence, we previously demonstrated that schizophrenia is associated with abnormal patterns of stimulus-evoked phaselocking of the electroencephalogram in the gamma band (30-100 Hz). These patterns may reflect impairments in neural assemblies, which have been proposed to use gamma-band oscillations as a mechanism for synchronization. Here, we report the unique finding that, in both healthy controls and schizophrenia patients, visual Gestalt stimuli elicit a gamma-band oscillation that is phase-locked to reaction time and hence may reflect processes leading to conscious perception of the stimuli. However, the frequency of this oscillation is lower in schizophrenics than in healthy individuals. This finding suggests that, although synchronization must occur for perception of the Gestalt, it occurs at a lower frequency because of a reduced capability of neural networks to support high-frequency synchronization in the brain of schizophrenics. Furthermore, the degree of phase locking of this oscillation is correlated with visual hallucinations, thought disorder, and disorganization in the schizophrenia patients. These data provide support for linking dysfunctional neural circuitry and the core symptoms of schizophrenia.

IDM COMMENT: NOTE ASSOCIATION TO SYNCHRONISATIONS - INDICATES SOMA AND SO MEDIATION "ISSUES" WHERE THE CHOICES OF REPRESENTATION ARE TOO MUCH OR "OUT OF BOUNDS".

Nat Rev Neurosci. 2001 Oct;2(10):704-16.

Dynamic predictions: oscillations and synchrony in top-down processing.

Engel AK, Fries P, Singer W.

Cellular Neurobiology Group, Institute for Medicine, Research Centre Julich, 52425 Julich, Germany. a.k.engel@fz-juelich.de

Classical theories of sensory processing view the brain as a passive, stimulus-driven device. By contrast, more recent approaches emphasize the constructive nature of perception, viewing it as an active and highly selective process. Indeed, there is ample evidence that the processing of stimuli is controlled by top-down influences that strongly shape the intrinsic dynamics of thalamocortical networks and constantly create predictions about forthcoming sensory events. We discuss recent experiments indicating that such predictions might be embodied in the temporal structure of both stimulus-evoked and ongoing activity, and that synchronous oscillations are particularly important in this process. Coherence among subthreshold membrane potential fluctuations could be exploited to express selective functional relationships during states of expectancy or attention, and these dynamic patterns could allow the grouping and selection of distributed neuronal responses for further processing.

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Neuron. 2004 Apr 22;42(2):335-46.

A Touching Sight; SII/PV Activation during the Observation and Experience of Touch.

Keysers C, Wicker B, Gazzola V, Anton JL, Fogassi L, Gallese V.

BCN Neuroimaging Centre, University of Groningen, 9713 AW Groningen, The Netherlands.

Watching the movie scene in which a tarantula crawls on James Bond's chest can make us literally shiver-as if the spider crawled on our own chest. What neural mechanisms are responsible for this "tactile empathy"? The observation of the actions of others activates the premotor cortex normally involved in the execution of the same actions. If a similar mechanism applies to the sight of touch, movies depicting touch should automatically activate the somatosensory cortex of the observer. Here we found using fMRI that the secondary but not the primary somatosensory cortex is activated both when the participants were touched and when they observed someone or something else getting touched by objects. The neural mechanisms enabling our own sensation of touch may therefore be a window also to our understanding of touch.

Neuron. 2003 Oct 30;40(3):655-64.

Both of us disgusted in My insula: the common neural basis of seeing and feeling disgust.

Wicker B, Keysers C, Plailly J, Royet JP, Gallese V, Rizzolatti G.

Institut de Neurosciences Physiologiques et Cognitives, CNRS, Chemin Joseph Aiguier, 13402 cedex 20, Marseille, France.

What neural mechanism underlies the capacity to understand the emotions of others? Does this mechanism involve brain areas normally involved in experiencing the same emotion? We performed an fMRI study in which participants inhaled odorants producing a strong feeling of disgust. The same participants observed video clips showing the emotional facial expression of disgust. Observing such faces and feeling disgust activated the same sites in the anterior insula and to a lesser extent in the anterior cingulate cortex. Thus, as observing hand actions activates the observer's motor representation of that action, observing an emotion activates the neural representation of that emotion. This finding provides a unifying mechanism for understanding the behaviors of others.

J Theor Biol. 2003 Feb 7;220(3):345-57.

Reputation and the evolution of conflict.

McElreath R.

Department of Anthropology, University of California, Davis, One Shields Avenue, Davis, CA 95616-8522, USA. mcelreath@davis.edu

The outcomes of conflicts in many human societies generate reputation effects that influence the nature of later conflicts. Those willing to escalate over even trivial offenses are considered honorable whereas those who do not are considered dishonorable (Nisbett & Cohen, 1996). Here I extend Maynard Smith's hawk-dove model of animal conflict to explore the logic of a strategy which uses reputation about its opponents to regulate its behavior. I show that a reputation-based strategy does well when (1) the value of the resource is large relative to the cost of losing a fight, (2) communities are stable, and (3) reputations are well known but subject to some amount of error. Reputation-based strategies may thus result in greater willingness to fight, but less fighting at equilibrium, depending upon the nature of the contests and the local socioecology. Additionally, this strategy is robust in the presence of poor knowledge about reputation.

J Pers Soc Psychol. 2003 Aug;85(2):363-72.

Conversing across cultures: East-West communication styles in work and nonwork contexts.

Sanchez-Burks J, Lee F, Choi I, Nisbett R, Zhao S, Koo J.

Business School and Institute of Social Research, University of Michigan, Ann Arbor 48109, USA. jeffrysb@umich.edu

Four experiments provided evidence that East-West differences in attention to indirect meaning are more pronounced in work settings compared with nonwork settings as suggested by prior research on Protestant relational ideology. Study 1 compared errors in interpreting indirect messages in work and nonwork contexts across three cultures. Studies 2 and 3 examined differences in self-reported indirectness with coworkers versus nonwork acquaintances across three cultures controlling for variation in individualism--collectivism. Study 4 examined self-reported indirectness in bicultural managers and experimentally manipulated the salience of Western versus Eastern culture. The results showed that Americans, but not East Asians, were less attentive to indirect cues in work than nonwork settings and that East-West differences in indirectness were greater in work than nonwork settings.

: Proc Natl Acad Sci U S A. 2003 Sep 16;100(19):11163-70. Epub 2003 Sep 05.

Culture and point of view.

Nisbett RE, Masuda T.

Department of Psychology, University of Michigan, Ann Arbor, MI 48109, USA. nisbett@umich.edu

East Asians and Westerners perceive the world and think about it in very different ways. Westerners are inclined to attend to some focal object, analyzing its attributes and categorizing it in an effort to find out what rules govern its behavior. Rules used include formal logic. Causal attributions tend to focus exclusively on the object and are therefore often mistaken. East Asians are more likely to attend to a broad perceptual and conceptual field, noticing relationships and changes and grouping objects based on family resemblance rather than category membership. Causal attributions emphasize the context. Social factors are likely to be important in directing attention. East Asians live in complex social networks with prescribed role relations. Attention to context is important to effective functioning. More independent Westerners live in less constraining social worlds and have the luxury of attending to the object and their goals with respect to it. The physical "affordances" of the environment may also influence perception. The built environments of the East are more complex and contain more objects than do those of the West. In addition, artistic products of the East emphasize the field and deemphasize individual objects, including people. Western art renders less of the field and emphasizes individual objects and people.

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NeuroImage
Volume 20, Issue 4 , December 2003, Pages 2181-2196

Copyright © 2003 Elsevier Inc. All rights reserved.

Multilingualism: an fMRI study

Guy Vingerhoetsa, John Van Borsel, , b, Cathelijne Tesinka, Maurits van den Noorta, Karel Deblaerec, Ruth Seurincka, Pieter Vandemaelec and Eric Achtenc

a Laboratory for Neuropsychology, Ghent University, Ghent, Belgium
b ENT-Department, Ghent University Hospital, Ghent, Belgium
c Department of Radiology, Ghent University, Ghent, Belgium

Received 17 December 2002; revised 3 July 2003; accepted 11 July 2003. ; Available online 14 November 2003.

Abstract
To investigate the hypothesis that in multilingual speakers different languages are represented in distinct brain regions, 12 multilingual right-handed men performed a word fluency task, a picture naming task, a comprehension reading task, and their respective control tasks in three languages (Dutch, French, and English) while whole-head functional magnetic resonance imaging (fMRI) was applied. In general, all language tasks revealed predominantly overlapping regions of activation for the different languages. Cerebral activation during use of the foreign languages showed a tendency toward a more extensive recruitment of the areas activated in the native language and the activation of a greater number of regions. Word generation in the foreign languages elicited additional bilateral inferior frontal activation, including Broca's area and left middle temporal gyrus activation; in the native language, additional postcentral activation was found. Picture naming in the foreign languages recruited additional inferior-lateral and medial frontal regions predominantly on the left, and more posterior right hemispheric activation in the mother tongue. During comprehension reading there was more activation in medial posterior regions in the native language. Our results suggest that the performance of language tasks in different languages engages largely the same cerebral areas but that the brain, to perform at a comparable proficiency level, engages more neural substrates for later acquired languages. Our findings do not support the view that languages learned later in life entail more right hemispheric involvement. Finally, a consequent effect of language exposure was found for reading, where increased familiarity engages more occipital activation whereas decreased familiarity appears to be associated with increased left hemispheric inferior frontal activation.

NeuroImage
Volume 20, Issue 4 , December 2003, Pages 2119-2125

Copyright © 2003 Elsevier Inc. All rights reserved.
Regular article

One brain, two selves

A. A. T. S. Reinders, , a, E. R. S. Nijenhuisb, A. M. J. Paansc, J. Korfa, A. T. M. Willemsenc and J. A. den Boera

a Department of Biological Psychiatry, Groningen University Hospital, The Netherlands
b Mental Health Care (Assen)/Cats-Polm Institute (Zeist), The Netherlands
c PET-center, Groningen University Hospital, The Netherlands

Received 12 May 2003; revised 6 July 2003; accepted 18 August 2003. ; Available online 14 November 2003.

Abstract
Having a sense of self is an explicit and high-level functional specialization of the human brain. The anatomical localization of self-awareness and the brain mechanisms involved in consciousness were investigated by functional neuroimaging different emotional mental states of core consciousness in patients with Multiple Personality Disorder (i.e., Dissociative Identity Disorder (DID)). We demonstrate specific changes in localized brain activity consistent with their ability to generate at least two distinct mental states of self-awareness, each with its own access to autobiographical trauma-related memory. Our findings reveal the existence of different regional cerebral blood flow patterns for different senses of self. We present evidence for the medial prefrontal cortex (MPFC) and the posterior associative cortices to have an integral role in conscious experience.

In two minds: dual-process accounts of reasoning
Jonathan St. B.T. Evans
Centre for Thinking and Language, University of Plymouth, Plymouth, PL4 8AA, UK

Researchers in thinking and reasoning have proposed
recently that there are two distinct cognitive systems
underlying reasoning. System 1 is old in evolutionary
terms and shared with other animals: it comprises a set
of autonomous subsystems that include both innate
input modules and domain-specific knowledge acquired
by a domain-general learning mechanism. System 2 is
evolutionarily recent and distinctively human: it permits
abstract reasoning and hypothetical thinking, but is
constrained by working memory capacity and corre-lated
with measures of general intelligence. These
theories essentially posit two minds in one brain with a
range of experimental psychological evidence showing
that the two systems compete for control of our infer-ences
and actions.

Psychosom Med. 2003 Jul-Aug;65(4):564-70.

Alterations in brain and immune function produced by mindfulness meditation.

Davidson RJ, Kabat-Zinn J, Schumacher J, Rosenkranz M, Muller D, Santorelli SF, Urbanowski F, Harrington A, Bonus K, Sheridan JF.

Laboratory for Affective Neuroscience (R.J.D., J.S., M.R.), Department of Psychology, University of Wisconsin, Madison, Wisconsin.

OBJECTIVE: The underlying changes in biological processes that are associated with reported changes in mental and physical health in response to meditation have not been systematically explored. We performed a randomized, controlled study on the effects on brain and immune function of a well-known and widely used 8-week clinical training program in mindfulness meditation applied in a work environment with healthy employees. METHODS: We measured brain electrical activity before and immediately after, and then 4 months after an 8-week training program in mindfulness meditation. Twenty-five subjects were tested in the meditation group. A wait-list control group (N = 16) was tested at the same points in time as the meditators. At the end of the 8-week period, subjects in both groups were vaccinated with influenza vaccine. RESULTS: We report for the first time significant increases in left-sided anterior activation, a pattern previously associated with positive affect, in the meditators compared with the nonmeditators. We also found significant increases in antibody titers to influenza vaccine among subjects in the meditation compared with those in the wait-list control group. Finally, the magnitude of increase in left-sided activation predicted the magnitude of antibody titer rise to the vaccine. CONCLUSIONS: These findings demonstrate that a short program in mindfulness meditation produces demonstrable effects on brain and immune function. These findings suggest that meditation may change brain and immune function in positive ways and underscore the need for additional research.

J Abnorm Psychol. 2002 Nov;111(4):676-81.

Frontal brain asymmetry in restrained eaters.

Silva JR, Pizzagalli DA, Larson CL, Jackson DC, Davidson RJ.

Psychobiology Department, Complutense University, Madrid, Spain.

It is well known that the eating patterns that restrain chronic dieters (restrained eaters) can be disinhibited by anxiety, which in turn has been associated with relative right frontal brain activity in independent electroencephalographic (EEG) studies. Combining these two lines of evidence, the authors tested the hypothesis that chronic restrained eating is associated with relative right frontal asymmetry. Resting anterior brain asymmetry and self-reported measures of anxiety and depression were collected in 23 restrained and 32 unrestrained eaters. As hypothesized, groups differed in tonic frontal activity, with restrained eaters showing more relative right frontal activity. Furthermore, relative right frontal activity was associated with greater self-reported restraint. Right-sided prefrontal asymmetry may thus represent a diathesis associated with increased vulnerability toward restrained eating.

Arch Gen Psychiatry. 2003 Aug;60(8):789-96.

Life event dimensions of loss, humiliation, entrapment, and danger in the prediction of onsets of major depression and generalized anxiety.

Kendler KS, Hettema JM, Butera F, Gardner CO, Prescott CA.

Virginia Institute for Psychiatry and Behavioral Genetics, Medical College of Virginia of Virginia Commonwealth University, Richmond, USA.

BACKGROUND: Although substantial evidence suggests that stressful life events predispose to the onset of episodes of depression and anxiety, the essential features of these events that are depressogenic and anxiogenic remain uncertain. METHODS: High contextual threat stressful life events, assessed in 98 592 person-months from 7322 male and female adult twins ascertained from a population-based registry, were blindly rated on the dimensions of humiliation, entrapment, loss, and danger and their categories. Onsets of pure major depression (MD), pure generalized anxiety syndrome (GAS) (defined as generalized anxiety disorder with a 2-week minimum duration), and mixed MD-GAS episodes were examined using logistic regression. RESULTS: Onsets of pure MD and mixed MD-GAS were predicted by higher ratings of loss and humiliation. Onsets of pure GAS were predicted by higher ratings of loss and danger. High ratings of entrapment predicted only onsets of mixed episodes. The loss categories of death and respondent-initiated separation predicted pure MD but not pure GAS episodes. Events with a combination of humiliation (especially other-initiated separation) and loss were more depressogenic than pure loss events, including death. No sex differences were seen in the prediction of episodes of illness by event categories. CONCLUSIONS: In addition to loss, humiliating events that directly devalue an individual in a core role were strongly linked to risk for depressive episodes. Event dimensions and categories that predispose to pure MD vs pure GAS episodes can be distinguished with moderate specificity. The event dimensions that preceded mixed MD-GAS episodes were largely the sum of those that preceded pure MD and pure GAS episodes.

Published online before print June 5, 2003
Proc. Natl. Acad. Sci. USA, 10.1073/pnas.0732061100

Neuroscience
Reset of human neocortical oscillations during a working memory task

D. S. Rizzuto *, J. R. Madsen , E. B. Bromfield ¶, A. Schulze-Bonhage ||, D.
Seelig *, R. Aschenbrenner-Scheibe ||, and M. J. Kahana ***
*Volen Center for Complex Systems, Brandeis University, Waltham, MA 02454;
Department of Neurosurgery, Children's Hospital, Boston, MA 02115; Department
of Surgery, Harvard Medical School, Boston, MA 02115; ¶Department of Neurology,
Brigham and Women's Hospital, Boston, MA 02115; and ||Neurozentrum,
Universitaet Freiburg, D-79106 Freiburg, Germany

Communicated by Saul Sternberg, University of Pennsylvania, Philadelphia, PA,
April 8, 2003 (received for review May 22, 2002)

Both amplitude and phase of rhythmic slow-wave electroencephalographic activity
are physiological correlates of learning and memory in rodents. In humans,
oscillatory amplitude has been shown to correlate with memory; however, the
role of oscillatory phase in human memory is unknown. We recorded intracranial
electroencephalogram from human cortical and hippocampal areas while subjects
performed a short-term recognition memory task. On each trial, a series of four
list items was presented followed by a memory probe. We found agreement across
trials of the phase of oscillations in the 7- to 16-Hz range after randomly
timed stimulus events, evidence that these events either caused a phase shift
in the underlying oscillation or initiated a new oscillation. Phase locking in
this frequency range was not generally associated with increased poststimulus
power, suggesting that stimulus events reset the phase of ongoing oscillations.
Different stimulus classes selectively modulated this phase reset effect, with
topographically distinct sets of recording sites exhibiting preferential reset
to either probe items or to list items. These findings implicate the reset of
brain oscillations in human working memory.

Does the cerebellum contribute to specific aspects of attention?

Birgit Gottwald, , Zoran Mihajlovic, Barbara Wilde and Hubertus Maximilian Mehdorn

Neuropsychologia

Volume 41, Issue 11 , 2003, Pages 1452-1460

Abstract

We present data on attentional and neuropsychological functions of 16 patients with focal cerebellar lesions (13 tumours, 3 haematomas) compared to normative test data, and to 11 control subjects matched for age, gender, and years of education. Patients showed distinct deficits in qualitative aspects of a divided attention task, and in a working memory task. Performance in selective attention was unimpaired. The results support the concept that the cerebellum plays a role not only in motor, but also in higher cognitive functions. They are discussed on the basis of the idea that prediction and preparation are fundamental functions of the cerebellum. Therefore, the results confirm the idea that cerebellar lesions lead to reduced performance in specific attention tasks.

<<IDM - gets into the issues of precision - dopamine shows ties to integration WITHIN a differentiation, linking of parts to assert a whole etc,fine motor control etc etc >>

Conscious control over the content of unconscious cognition

Wilfried Kunde, Andrea Kiesel and Joachim Hoffmann

Cognition

Volume 88, Issue 2 , June 2003, Pages 223-242

Abstract

Visual stimuli (primes) presented too briefly to be consciously identified can nevertheless affect responses to subsequent stimuli – an instance of unconscious cognition. There is a lively debate as to whether such priming effects originate from unconscious semantic processing of the primes or from reactivation of learned motor responses that conscious stimuli afford during preceding practice. In four experiments we demonstrate that unconscious stimuli owe their impact neither to automatic semantic categorization nor to memory traces of preceding stimulus-response episodes, but to their match with pre-specified cognitive action-trigger conditions. The intentional creation of such triggers allows actors to control the way unconscious stimuli bias their behaviour.

Dissociable neural systems for recognizing emotions

- Ralph Adolphs, Daniel Tranel and Antonio R. Damasio

Brain and Cognition

Volume 52, Issue 1 , June 2003, Pages 61-69

Abstract

This study tested the hypothesis that the recognition of emotions would draw upon anatomically separable brain regions, depending on whether the stimuli were static or explicitly conveyed information regarding actions. We investigated the hypothesis in a rare subject with extensive bilateral brain lesions, patient B., by administering tasks that assessed recognition and naming of emotions from visual and verbal stimuli, some of which depicted actions and some of which did not. B. could not recognize any primary emotion other than happiness, when emotions were shown as static images or given as single verbal labels. By contrast, with the notable exception of disgust, he correctly recognized primary emotions from dynamic displays of facial expressions as well as from stories that described actions. Our findings are consistent with the idea that information about actions is processed in occipitoparietal and dorsal frontal cortices, all of which are intact in B.'s brain. Such information subsequently would be linked to knowledge about emotions that depends on structures mapping somatic states, many of which are also intact in B.'s brain. However, one of these somatosensory structures, the insula, is bilaterally damaged, perhaps accounting for B.'s uniformly impaired recognition of disgust (from both static and action stimuli). Other structures that are damaged in B.'s brain, including bilateral inferior and anterior temporal lobe and medial frontal cortices, appear to be critical for linking perception of static stimuli to recognition of emotions. Thus the retrieval of knowledge regarding emotions draws upon widely distributed and partly distinct sets of neural structures, depending on the attributes of the stimulus.

Brain Res Bull. 2003 May 30;60(4):387-93.

The evolution of mammalian cortex, from lamination to arealization.

Montagnini A, Treves A.

SISSA-Programme in Neuroscience, via Beirut 4, 34014, Trieste, Italy

We analyse some of the most important anatomical and functional features emerging at different stages of mammalian brain evolution in terms of a possible computational advantage. At the transition from reptiles to mammals, a major anatomical change occurs in the originally sensory dorsal cortex. The principal layer of pyramidal cells is split by the insertion of a new layer of granule cells, giving rise to the laminated isocortex. It has been hypothesized that this qualitative change in the evolution of mammalian brains is necessary to support fine topography in their sensory maps. The simulation of neural network models demonstrates that a nonlaminated patch of cortex must compromise between transmitting "where" information, explicitly mapped, topographically, on the cortical sheet, and retrieving "what" information, represented by the distributed firing pattern across neurons. The differentiation of a granular layer is shown in the model to yield a small quantitative advantage, allowing to transmit a slightly better combination of both information types.Along the same theoretical lines, we are investigating the multiplication of successive sensory areas coding for ever more composite stimuli, such as those in the visual and auditory temporal cortices in primates. In particular we analyse the possible computational advantage for a specific neural population devoted to encode the complex structure of whole stimuli, rather than relying on the coactivation of separate populations encoding their basic elements.

Cell. 2003 Feb 7;112(3):293-301.

Coding of sweet, bitter, and umami tastes: different receptor cells sharing similar signaling pathways.

Zhang Y, Hoon MA, Chandrashekar J, Mueller KL, Cook B, Wu D, Zuker CS, Ryba NJ.

Howard Hughes Medical Institute, Department of Biology, University of California, San Diego, La Jolla, CA 92093, USA.

Mammals can taste a wide repertoire of chemosensory stimuli. Two unrelated families of receptors (T1Rs and T2Rs) mediate responses to sweet, amino acids, and bitter compounds. Here, we demonstrate that knockouts of TRPM5, a taste TRP ion channel, or PLCbeta2, a phospholipase C selectively expressed in taste tissue, abolish sweet, amino acid, and bitter taste reception, but do not impact sour or salty tastes. Therefore, despite relying on different receptors, sweet, amino acid, and bitter transduction converge on common signaling molecules. Using PLCbeta2 taste-blind animals, we then examined a fundamental question in taste perception: how taste modalities are encoded at the cellular level. Mice engineered to rescue PLCbeta2 function exclusively in bitter-receptor expressing cells respond normally to bitter tastants but do not taste sweet or amino acid stimuli. Thus, bitter is encoded independently of sweet and amino acids, and taste receptor cells are not broadly tuned across these modalities.

J Neurophysiol 2002 Jun;87(6):2715-25

Stimulus-related gamma oscillations in primate auditory cortex.

Brosch M, Budinger E, Scheich H.

Leibniz-Institut fur Neurobiologie, 39118 Magdeburg, Germany. brosch@ifn-magdeburg.de

With a multielectrode system, we explored neuronal activity in the gamma range (>40 Hz) in the primary and caudomedial auditory cortex of six anesthetized macaque monkeys. Stimuli were tone bursts of 100- to 500-ms duration that were presented at sound pressure levels of 40-60 dB and were varied over a wide range of frequencies. These stimuli induced gamma oscillations, not phase-locked to the onset of stimulation, in 465 of 616 multiunit clusters and at 321 of 422 sites at which field potentials were recorded. Occurrence of gamma activity was stimulus dependent. It was mostly seen when the stimulus was at the units' preferred frequency. The incidence of gamma activity decreased with increasing difference between stimulus frequency and preferred frequency. gamma activity emerged 100-900 ms after stimulus onset with highest incidence ~120 ms. Amplitudes of stimulus-induced gamma oscillations in field potentials were, on average, almost twice the amplitude of spontaneously occurring gamma oscillations. gamma activity at different sites within the primary and the caudomedial auditory field could be synchronized at near-zero phase. Synchrony depended on the spatial distance and on the receptive fields similarity of pairs of units. It decreased with increasing distance between recording sites and increased with similarity of preferred frequencies of the pairs of units. The results indicate that stimulus-induced gamma oscillations originate from sources in the auditory cortex. They further suggest that gamma oscillations may provide a mechanism utilized in many parts of the sensory cortex, including the auditory cortex, to integrate neurons according to the similarity of their receptive fields.

International Journal of Bifurcation and Chaos, Vol. 13, No. 1 (2003) 7-18

WHEN TWO COUPLED PENDULUMS EQUAL ONE: A SYNCHRONIZATION MACHINE

H. J. T. SMITH
Department of Physics, University of Waterloo, Ontario, Canada

JAMES A. BLACKBURN
Department of Physics and Computing, Wilfrid Laurier University, Waterloo, Ontario, Canada

GREGORY L. BAKER
Division of Mathematics and Science, Bryn Athyn College of the New Church, Bryn Athyn, PA 19009, USA
We show that two coupled pendulums that are coupled and can synchronize, are mathematically equivalent to one "horizontal" parametrically driven pendulum. We have fabricated a horizontal pendulum and present data from this horizontal pendulum which we believe to be the first physical realization of such a mechanical "synchronization machine." A description of intermittent synchronization that can occur when two coupled pendulums are in a chaotic state is given in terms of the data from the horizontal pendulum. We discuss the relationship between the modes of the horizontal pendulum and the corresponding synchronization of the two coupled pendulums. Finally, we show that when a horizontal pendulum is driven by any random source, not necessarily chaotic, intermittent synchronization can occur.

Keywords: Pendulum; synchronization; chaos.

Brain Res Brain Res Rev 2002 Jun;39(1):1-28

The neurophysics of consciousness.

John ER.

Brain Research Laboratories, NYU School of Medicine, 550 First Avenue, New York 10016, USA. roy@br14.med.nyu.edu

Consciousness combines information about attributes of the present multimodal sensory environment with relevant elements of the past. Information from each modality is continuously fractionated into distinct features, processed locally by different brain regions relatively specialized for extracting these disparate components and globally by interactions among these regions. Information is represented by levels of synchronization within neuronal populations and of coherence among multiple brain regions that deviate from random fluctuations. Significant deviations constitute local and global negative entropy, or information. Local field potentials reflect the degree of synchronization among the neurons of the local ensembles. Large-scale integration, or 'binding', is proposed to involve oscillations of local field potentials that play an important role in facilitating synchronization and coherence, assessed by neuronal coincidence detectors, and parsed into perceptual frames by cortico-thalamo-cortical loops. The most probable baseline levels of local synchrony, coherent interactions among brain regions, and frame durations have been quantitatively described in large studies of their age-appropriate normative distributions and are considered as an approximation to a conscious 'ground state'. The level of consciousness during anesthesia can be accurately predicted by the magnitude and direction of reversible multivariate deviations from this ground state. An invariant set of changes takes place during anesthesia, independent of the particular anesthetic agent. Evidence from a variety of neuroscience areas supporting these propositions, together with the invariant reversible electrophysiological changes observed with loss and return of consciousness, are used to provide a foundation for this theory of consciousness. This paper illustrates the increasingly recognized need to consider global as well as local processes in the search for better explanations of how the brain accomplishes the transformation from synchronous and distributed neuronal discharges to seamless global subjective awareness.

J Neurophysiol 2002 Apr;87(4):1993-2008

GABAergic and glutamatergic modulation of spontaneous and motor-cortex-evoked complex spike activity.

Lang EJ.

Department of Physiology and Neuroscience, New York University School of Medicine, New York, New York 10016, USA. Lange01@popmail.med.nyu.edu

Olivocerebellar activity is organized such that synchronous complex spikes occur primarily among Purkinje cells located within the same parasagittally oriented strip of cortex. Previous findings have shown that this synchrony distribution is modulated by the release of GABA and glutamate within the inferior olive, which probably act by controlling the efficacy of the electrotonic coupling between olivary neurons. The relative strengths of these two neurotransmitters in modulating the patterns of synchrony were compared by obtaining multiple electrode recordings of spontaneous crus 2a complex spike activity during intraolivary injection of solutions containing a GABA(A) (picrotoxin) and/or AMPA [1,2,3,4-tetrahydro-6-nitro-2,3-dioxo-benzo[f]quinoxaline-7-sulfonamide disodium (NBQX)] receptor antagonist. Injection of either antagonist led to increased synchrony between cells located within the same parasagittally oriented approximately 250-microm-wide cortical strip. Picrotoxin also increased complex spike synchrony among cells located in different cortical strips, leading to a less prominent banding pattern, whereas injections of NBQX tended to decrease complex spike synchrony among such cells, enhancing the banding pattern. The relative strength of these two classes of olivary afferents was assessed by first injecting one of the antagonists alone and then in combination with the other. The enhanced banding pattern of complex spike synchrony following injection of NBQX alone remained during the subsequent combined injection of both antagonists. Furthermore, the widespread synchronization of complex spike activity following injection of picrotoxin alone was partially or completely reversed by combined injection of picrotoxin and NBQX. Changes in the climbing fiber reflex induced by the intraolivary injections paralleled the changes observed for spontaneous complex spike activity, indicating that the effects of picrotoxin and NBQX on the synchrony distribution reflect changes in the pattern of effective coupling of inferior olivary neurons and demonstrating that synchronous complex spike activity does not require simultaneous excitatory input to olivary cells. Finally the pattern of synchrony during motor cortical stimulation was examined. It was found that the patterns of synchrony for motor-cortex-evoked complex spike activity were similar to those of spontaneous activity, indicating an important role for electrotonic coupling in determining the response of the olivocerebellar system to afferent input. Moreover, intraolivary injections of picrotoxin increased the spatial distribution of the evoked response. In sum, the results provide evidence for the hypothesis that electrotonic coupling of inferior olivary neurons via gap junctions is the mechanism underlying complex spike synchrony and that this coupling plays an important role in determining the responses of the olivocerebellar system to synaptic input.

J Neurosci 2002 Feb 1;22(3):1002-9

Electrical synapses in the thalamic reticular nucleus.

Landisman CE, Long MA, Beierlein M, Deans MR, Paul DL, Connors BW.

Department of Neuroscience, Division of Biology and Medicine, Brown University, Providence, Rhode Island 02912, USA.

Neurons of the thalamic reticular nucleus (TRN) provide inhibitory input to thalamic relay cells and generate synchronized activity during sleep and seizures. It is widely assumed that TRN cells interact only via chemical synaptic connections. However, we show that many neighboring pairs of TRN neurons in rats and mice are electrically coupled. In paired-cell recordings, electrical synapses were able to mediate close correlations between action potentials when the coupling was strong; they could modulate burst-firing states even when the coupling strength was more modest. Electrical synapses between TRN neurons were absent in mice with a null mutation for the connexin36 (Cx36) gene. Surprisingly, inhibitory chemical synaptic connections between pairs of neurons were not observed, although strong extracellular stimuli could evoke inhibition in single TRN neurons. We conclude that Cx36-dependent gap junctions play an important role in the regulation of neural firing patterns within the TRN. When combined with recent observations from the cerebral cortex, our results imply that electrical synapses are a common mechanism for generating synchrony within networks of inhibitory neurons in the mammalian forebrain.

J Neurophysiol 2002 Mar;87(3):1526-41

Electrical coupling between model midbrain dopamine neurons: effects on firing pattern and synchrony.

Komendantov AO, Canavier CC.

Department of Psychology, University of New Orleans, New Orleans, LA 70148, USA.

The role of gap junctions between midbrain dopamine (DA) neurons in mechanisms of firing pattern generation and synchronization has not been well characterized experimentally. We modified a multi-compartment model of DA neuron by adding a spike-generating mechanism and electrically coupling the dendrites of two such neurons through gap junctions. The burst-generating mechanism in the model neuron results from the interaction of a N-methyl-D-aspartate (NMDA)-induced current and the sodium pump. The firing patterns exhibited by the two model neurons included low frequency (2-7 Hz) spiking, high-frequency (13-20 Hz) spiking, irregular spiking, regular bursting, irregular bursting, and leader/follower bursting, depending on the parameter values used for the permeability for NMDA-induced current and the conductance for electrical coupling. All of these firing patterns have been observed in physiological neurons, but a systematic dependence of the firing pattern on the covariation of these two parameters has not been established experimentally. Our simulations indicate that electrical coupling facilitates NMDA-induced burst firing via two mechanisms. The first can be observed in a pair of identical cells. At low frequencies (low NMDA), as coupling strength was increased, only a transition from asynchronous to synchronous single-spike firing was observed. At high frequencies (high NMDA), increasing the strength of the electrical coupling in an identical pair resulted in a transition from high-frequency single-spike firing to burst firing, and further increases led to synchronous high-frequency spiking. Weak electrical coupling destabilizes the synchronous solution of the fast spiking subsystems, and in the presence of a slowly varying sodium concentration, the desynchronized spiking solution leads to bursts that are approximately in phase with spikes that are not in phase. Thus this transitional mechanism depends critically on action potential dynamics. The second mechanism for the induction of burst firing requires a heterogeneous pair that is, respectively, too depolarized and too hyperpolarized to burst. The net effect of the coupling is to bias at least one cell into an endogenously burst firing regime. In this case, action potential dynamics are not critical to the transitional mechanism. If electrical coupling is indeed more prominent in vivo due to basal level of modulation of gap junctions in vivo, these results may indicate why NMDA-induced burst firing is easier to observe in vivo as compared in vitro.

Neurosci Lett 2003 Jan 9;336(1):33-6

Scale-invariant fluctuations of the dynamical synchronization in human brain electrical activity.

Gong P, Nikolaev AR, van Leeuwen C.

Laboratory for Perceptual Dynamics, Riken, Brain Science Institute, 2-1, Hirosawa, Wako-shi, Saitama, 351-0198, Japan. plgong@brain.riken.go.jp

The dynamical properties of large-scale, long-term phase synchronization behavior in the alpha range of electroencephalographic signals were investigated. We observed dynamical phase synchronization and presented evidence of an underlying spatiotemporal ordering. Fluctuations in the duration of episodes of intermittent synchrony are scale-invariant. Moreover, the exponent used to describe this behavior is stable across different normal subjects. The results provide a new feature of self-organization in human brain activity and constitute a quantitative basis for modeling its dynamics.
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Epilepsia 2002 Jun;43(6):574-80

Cooling abolishes neuronal network synchronization in rat hippocampal slices.

Javedan SP, Fisher RS, Eder HG, Smith K, Wu J.

Division of Neurological Surgery, Barrow Neurological Institute, St. Joseph's Hospital and Medical Center, Phoenix, Arizona 85013, USA.

PURPOSE: We sought to determine whether cooling brain tissue from 34 to 21 degrees C could abolish tetany-induced neuronal network synchronization (gamma oscillations) without blocking normal synaptic transmission. METHODS: Intracellular and extracellular electrodes recorded activity in transverse hippocampal slices (450-500 microm) from Sprague-Dawley male rats, maintained in an air-fluid interface chamber. Gamma oscillations were evoked by afferent stimulation at 100 Hz for 200 ms. Baseline temperature in the recording chamber was 34 degrees C, reduced to 21 degrees C within 20 min. RESULTS: Suprathreshold tetanic stimuli evoked membrane potential oscillations in the 40-Hz frequency range (n = 21). Gamma oscillations induced by tetanic stimulation were blocked by bicuculline, a gamma-aminobutyric acid (GABA)A-receptor antagonist. Cooling from 34 to 21 degrees C reversibly abolished gamma oscillations in all slices tested. Short, low-frequency discharges persisted after cooling in six of 14 slices. Single-pulse-evoked potentials, however, were preserved after cooling in all cases. Latency between stimulus and onset of gamma oscillation was increased with cooling. Frequency of oscillation was correlated with chamber cooling temperature (r = 0.77). Tetanic stimulation at high intensity elicited not only gamma oscillation, but also epileptiform bursts. Cooling dramatically attenuated gamma oscillation and abolished epileptiform bursts in a reversible manner. CONCLUSIONS: Tetany-induced neuronal network synchronization by GABAA-sensitive gamma oscillations is abolished reversibly by cooling to temperatures that do not block excitatory synaptic transmission. Cooling also suppresses transition from gamma oscillation to ictal bursting at higher stimulus intensities. These findings suggest that cooling may disrupt network synchrony necessary for epileptiform activity.

Nature 2002 Nov 14;420(6912):168-71

Synchronization of animal population dynamics by large-scale climate.

Post E, Forchhammer MC.

Department of Biology, The Pennsylvania State University, 208 Mueller Lab, University Park, Pennsylvania 16802, USA. esp10@psu.edu

The hypothesis that animal population dynamics may be synchronized by climate is highly relevant in the context of climate change because it suggests that several populations might respond simultaneously to climatic trends if their dynamics are entrained by environmental correlation. The dynamics of many species throughout the Northern Hemisphere are influenced by a single large-scale climate system, the North Atlantic Oscillation (NAO), which exerts highly correlated regional effects on local weather. But efforts to attribute synchronous fluctuations of contiguous populations to large-scale climate are confounded by the synchronizing influences of dispersal or trophic interactions. Here we report that the dynamics of caribou and musk oxen on opposite coasts of Greenland show spatial synchrony among populations of both species that correlates with the NAO index. Our analysis shows that the NAO has an influence in the high degree of cross-species synchrony between pairs of caribou and musk oxen populations separated by a minimum of 1,000 km of inland ice. The vast distances, and complete physical and ecological separation of these species, rule out spatial coupling by dispersal or interaction. These results indicate that animal populations of different species may respond synchronously to global climate change over large regions.

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Biosystems 2002 Oct-Dec;67(1-3):139-46

Firing coincidences between neighboring retinal ganglion cells: inside information or epiphenomenon?

Levine MW, Castaldo K, Kasapoglu MB.

Department of Psychology, M/C 285, University of Illinois at Chicago, 1007 West Harrison Street, 60607, Chicago, IL, USA

Retinal ganglion cells often fire impulses in synchrony; is this synchronization an irrelevant by-product of processing shared inputs, or does it encode information? We examined the rate of occurrence of coincident impulses from pairs of ganglion cells responding to stimuli that varied along several dimensions. We find that coincidences convey little if any additional information about simple static stimuli beyond what could be determined from the firing rates of the two cells considered separately. In fact, at least one of the separate cells generally provided a better information channel than the coincidence rate, implying that under these conditions ganglion cells do not employ a strategy of encoding by coincidences.

J Neurosci 2002 Dec 15;22(24):10898-905

Rhythmicity without synchrony in the electrically uncoupled inferior olive.

Long MA, Deans MR, Paul DL, Connors BW.

Department of Neuroscience, Division of Biology and Medicine, Brown University, Providence, Rhode Island 02912, USA.

Neurons of the inferior olivary nucleus (IO) form the climbing fibers that excite Purkinje cells of the cerebellar cortex. IO neurons are electrically coupled through gap junctions, and they generate synchronous, subthreshold oscillations of membrane potential at approximately 5-10 Hz. Experimental and theoretical studies have suggested that both the rhythmicity and synchrony of IO neurons require electrical coupling. We recorded from pairs of IO neurons in slices of mouse brainstem in vitro. Most pairs of neurons from wild-type (WT) mice were electrically coupled, but coupling was rare and weak between neurons of knock-out (KO) mice for connexin36, a neuronal gap junction protein. IO cells in both WT and KO mice generated rhythmic membrane fluctuations of similar frequency and amplitude. Oscillations in neighboring pairs of WT neurons were strongly synchronized, whereas the oscillations of KO pairs were uncorrelated. Spontaneous oscillations in KO neurons were not blocked by tetrodotoxin. Spontaneously oscillating neurons of both WT and KO mice generated occasional action potentials in phase with their membrane rhythms, but only the action potentials of WT neuron pairs were synchronous. Harmaline, a beta-carboline derivative thought to induce tremor by facilitating rhythmogenesis in the IO, was injected systemically into WT and KO mice. Harmaline-induced tremors were robust and indistinguishable in the two genotypes, suggesting that gap junction-mediated synchrony does not play a role in harmaline-induced tremor. We conclude that electrical coupling is not necessary for the generation of spontaneous subthreshold oscillations in single IO neurons, but that coupling can serve to synchronize rhythmic activity among IO neurons.

Percept Mot Skills 2002 Dec;95(3 Pt 1):1013-26

The Mozart effect may only be demonstrable in nonmusicians.

Twomey A, Esgate A.

University of Westminster, London, UK.

The "Mozart effect" is the tendency to score higher on spatiotemporal IQ subscales following exposure to complex music such as Mozart's Sonata K.448. This phenomenon was investigated in 20 musicians and 20 nonmusicians. The trion model predicts increased synchrony between musical and spatiotemporal centres in the right cerebral hemisphere. Since increased left-hemispheric involvement in music processing occurs as a result of music training, predictions deriving from the possibility of increased synchrony with left-hemispheric areas in musicians were tested. These included improved performance on language as well as spatiotemporal tasks. Spatiotemporal, synonym generation, and rhyming word generation tasks were employed as was the Mozart Sonata K.448. A Mozart effect was demonstrated on the spatiotemporal task, and the facilitatory effect of exposure to Mozart was greater for the nonmusician group. This finding adds to the robustness of the Mozart effect since novel tasks were used. No Mozart effect was found for either group on the verbal tasks, although the musicians scored higher on rhyming word generation. This new finding adds to the number of nonmusical tasks apparently showing long-term benefits from music training. However, no systematic link was found between performance on any task and number of years spent in music training. The failure to induce a Mozart effect in the musician group on verbal tasks, as well as that group's limited facilitation on spatiotemporal tasks, may be associated with either a ceiling effect due to the long-term effects of music training or from methodological factors. Both possibilities are discussed.

Brain Res Brain Res Rev 2003 Jan;41(1):57-78

Synchronous gamma activity: a review and contribution to an integrative neuroscience model of schizophrenia.

Lee KH, Williams LM, Breakspear M, Gordon E.

Cognitive Neuroscience Unit, Department of Psychology, University of Sydney, and The Brain Dynamics Centre, Westmead Hospital, 2145, Sydney, NSW, Australia.

Synchronous high frequency (Gamma band) activity has been proposed as a candidate mechanism for the integration or 'binding' of distributed brain activities. Since the first descriptions of schizophrenia, attempts to characterize this disorder have focused on disturbances in such integrative processing. Here, we review both micro- and macroscopic neuroscience research into Gamma synchrony, and its application to understanding schizophrenia. The review encompasses evidence from both animal and human studies for the functional significance of Gamma activity, the association between Gamma dysfunction and information processing disturbances, and the relevance of specific Gamma dysfunctions to the integration and extension of previous disconnection models of schizophrenia. Attention is given to the relationship between Gamma activity and the heterogeneous symptoms of schizophrenia. Existing studies show that measures of Gamma activity have the potential to explain far more of the variance in schizophrenia performance than previous neurophysiological measures. It is concluded that measures of Gamma synchrony offer a valuable window into the core integrative disturbance in schizophrenia cognition.

(IDM FOCUS - gamma functions like a system clock, irregular timing leads to anomolies in encoding/decoding)

Clin Neurophysiol 2002 Oct;113(10):1640-6

Is 'gamma' (40 Hz) synchronous activity disturbed in patients with traumatic brain injury?

Slewa-Younan S, Green AM, Baguley IJ, Felmingham KL, Haig AR, Gordon E.

Brain Injury Rehabilitation Service, Westmead Hospital, PO Box 533, Wentworthville, NSW, 2145, Australia. shameran@biru.wsahs.nsw.gov.au

OBJECTIVES: The objective of this work is to determine whether Gamma (40 Hz) synchronous activity has disturbed patients with severe traumatic brain injury (TBI).METHODS: Using a conventional auditory oddball paradigm, the extent of Gamma synchrony across multiple scalp sites in specific frequency bands as a function of time was examined in 15 patients with severe TBI and 15 age- and sex-matched controls. Averaged Gamma synchrony was analyzed using within and between group multiple analyses of variance with region (left versus right hemisphere, anterior versus posterior region) as the within factor.RESULTS: Compared to controls, subjects with TBI displayed significantly delayed early Gamma latency (from -150 to 150 ms) (F((1,28))=10.28, P<0.003) across all sites in addition to other specific regional disturbances. For late Gamma synchrony, subjects with TBI displayed delayed Gamma latency at the left hemisphere (from 200 to 450 ms) (F((1,28))=8.71, P<0.006) and posterior region (F((1,28))=9.18, P<0.006) in comparison to controls.CONCLUSIONS: Impaired integration of spatially distributed brain activity ('40 Hz' electroencephalogram rhythms) may be an important marker of deficits of cortical network binding postulated to be abnormal in people who have survived TBI.

Naturwissenschaften 2002 Jul;89(7):316-8

Inter-cellular spike coincidences in visual detection tasks.

Bauer R, Heinze S.

FB Physik/Neurophysik, Philipps-Universitat, Marburg, Germany. roman.bauer@physik.uni-marburg.de

Synchronized spike activity is discussed as a possible representational code for object integration and as a neuronal basis of attention, perception and awareness. As a byproduct of experiments in which monkeys were trained to detect simple figures composed of single Gabor patches in a noisy background of similar elements, we found in special cases increased spike synchrony above chance level specifically related to figure detection. The long latency of this effect is difficult to interpret. It may be a sign of the cognitive state of an animal when it perceives the figure.
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: J Neurosci 2002 Jul 1;22(13):5694-704

Sleep states differentiate single neuron activity recorded from human epileptic hippocampus, entorhinal cortex, and subiculum.

Staba RJ, Wilson CL, Bragin A, Fried I, Engel J Jr.

Department of Neurobiology, David Greffen School of Medicine at University of California Los Angeles, Los Angeles, California 90095, USA.

Animal models of epilepsy have shown that synchronous burst firing is associated with epileptogenesis, yet the evidence from human studies linking neuronal synchrony and burst firing to epileptogenesis remains equivocal. Sleep-wake states have been shown to differentially modulate the generation of epileptiform EEG spikes between brain regions of greater and lesser seizure-generating potential, providing information that helps to identify the primary epileptogenic region. Using these state-dependent mechanisms to assist us in identifying neuronal correlates of human epilepsy, we recorded interictal neuronal activity from mesial temporal lobe (MTL) areas in epileptic patients implanted with depth electrodes required for medical diagnosis during polysomnographically defined sleep-wake states. Results show that single neurons recorded ipsilateral to seizure-initiating MTL ("epileptic") areas had significantly higher firing rates (p = 0.01) and burst propensity (p = 0.01) and greater synchrony of discharges (p = 0.003) compared with neurons recorded from contralateral non-seizure-generating MTL ("non-epileptic") areas. In particular, during episodes of slow wave sleep (SWS) and rapid eye movement (REM) sleep, epileptic hippocampal neurons had significantly higher burst rates compared with non-epileptic hippocampal neurons (both p = 0.01). In contrast, during episodes of wakefulness (Aw), no difference in burst firing between epileptic and non-epileptic hippocampal neurons was observed. Furthermore, synchronous firing was significantly higher between epileptic MTL neurons compared with non-epileptic MTL neurons during SWS (p = 0.04) and REM sleep (p = 0.02), but no difference in neuronal synchrony was found between epileptic and non-epileptic neurons during Aw. These results provide evidence that sleep states differentially modulate abnormal epileptogenic neuronal discharge properties within human MTL and confirm that neuronal burst firing and enhanced neuronal synchrony observed in experimental animal models of epilepsy characterizes human epilepsy as well.
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J Neurosci 2002 Jun 1;22(11):4639-53

Enhanced synchrony among primary motor cortex neurons in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine primate model of Parkinson's disease.

Goldberg JA, Boraud T, Maraton S, Haber SN, Vaadia E, Bergman H.

Department of Physiology, The Hebrew University-Hadassah Medical School, the Interdisciplinary Center for Neural Computation, The Hebrew University, Jerusalem 91120, Israel. joshg@md.huji.ac.il

Primary motor cortex (MI) neurons discharge vigorously during voluntary movement. A cardinal symptom of Parkinson's disease (PD) is poverty of movement (akinesia). Current models of PD thus hypothesize that increased inhibitory pallidal output reduces firing rates in frontal cortex, including MI, resulting in akinesia and muscle rigidity. We recorded the simultaneous spontaneous discharge of several neurons in the arm-related area of MI of two monkeys and in the globus pallidus (GP) of one of the two. Accelerometers were fastened to the forelimbs to detect movement, and surface electromyograms were recorded from the contralateral arm of one monkey. The recordings were conducted before and after systemic treatment with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), rendering the animals severely akinetic and rigid with little or no tremor. The mean spontaneous MI rates during periods of immobility (four to five spikes/sec) did not change after MPTP; however, in this parkinsonian state, MI neurons discharged in long bursts (sometimes >2 sec long). These bursts were synchronized across many cells but failed to elicit detectable movement, indicating that even robust synchronous MI discharge need not result in movement. These synchronized population bursts were absent from the GP and were on a larger timescale than oscillatory synchrony found in the GP of tremulous MPTP primates, suggesting that MI parkinsonian synchrony arises independently of basal ganglia dynamics. After MPTP, MI neurons responded more vigorously and with less specificity to passive limb movement. Abnormal MI firing patterns and synchronization, rather than reduced firing rates, may underlie PD akinesia and persistent muscle rigidity.

Ann N Y Acad Sci 2002 Dec;978:164-74

Temporal organization of activity in the cerebellar cortex: a manifesto for synchrony.

Isope P, Dieudonne S, Barbour B.

Laboratoire de Neurobiologie (CNRS UMR 8544), Ecole Normale Superieure, 75230 Paris Cedex 05, France.

The issues of temporal coding and the temporal organization of activity have aroused a great deal of interest in sensory systems, cortex, thalamus, and hippocampus. Strangely, despite the important timing roles attributed to the cerebellum, little consideration has been given to the organization of activity within the cerebellar circuitry. In fact, there is evidence of a remarkable temporal patterning of activity in even the earliest cerebellar recordings. The evidence for the existence of high-frequency oscillations in the cerebellar cortex is reviewed and possible mechanisms are discussed; one involves the synchrony of parallel fiber inputs to Purkinje cells. It is shown how synchronous and oscillatory activity can enable extremely precise timing and also how they can maximize the information storage capacity of the cerebellar cortex.

AJNR Am J Neuroradiol 2003 Feb;24(2):208-12

Role of the corpus callosum in functional connectivity.

Quigley M, Cordes D, Turski P, Moritz C, Haughton V, Seth R, Meyerand ME.

Department of Medical Physics, University of Wisconsin-Madison, 1300 University Avenue, 1530 MSC, Madison, WI 53706, USA.

BACKGROUND AND PURPOSE: Regional cerebral blood flow fluctuates synchronously in corresponding brain regions between the hemispheres. This synchrony implies neuronal connections between brain regions. The synchrony of blood flow changes is defined operationally as functional connectivity. Our purpose was to measure functional connectivity in patients with corpus callosal agenesis, in whom the interhemispheric connectivity is hypothetically diminished. METHODS: In three patients with agenesis of the corpus callosum, functional MR imaging was performed while patients performed text-listening and finger-tapping tasks. Functional images were also acquired while the patients performed no specific task (resting state). Regions of activation temporally correlated with the performance of the tasks were identified by cross-correlating the task data with a reference function. Voxel clusters (seed voxels) that corresponded to regions of activation in the task-activation data set were selected in the resting data set. All the voxels in the resting 3D data set that had a correlation coefficient exceeding 0.4 were identified. The number of these voxels in the ipsilateral and contralateral hemispheres was tabulated. RESULTS: In all patients, technically adequate functional MR and functional connectivity MR maps were obtained. For both tasks, activation was found in both hemispheres. For all of the seed voxels, significantly more functionally connected voxels were found in the ipsilateral hemisphere than in the contralateral hemisphere. For most seed voxels, no functionally connected voxels were found in the contralateral hemisphere. CONCLUSION: Interhemispheric functional connectivity in the motor and auditory cortices is diminished in patients with agenesis of the corpus callosum compared with that of healthy subjects.

Life Sci Space Res 1977;15:233-7

The effect of low light intensity on the maintenance of circadian synchrony in human subjects.

Winget CM, Lyman J, Beljan JR.

Biomedical Research Division, NASA, Ames Research Center, Moffett Field, Calif, USA.

The light-intensity threshold for humans is not known. In past space flights owing to power restrictions, light intensities have been minimal and reported to be as low as 15 ft. c. This study was conducted to determine whether the light (L)/dark (D) environment of 16L : 8D at the relatively low light intensity of 15 ft. c. was adequate for the maintenance of circadian synchrony in human subjects. Six healthy male subjects aged 20-23 years were exposed for 21 days to a 16L : 8D photoperiod. During the first 7 days the light intensity was 100 ft. c.; it was reduced to 15 ft. c. during the next 7 days and increased again to 100 ft. c. during the last 7 days of the study. Rectal temperature (RT) and heart rate (HR) were recorded continuously throughout the 21 days of the study. In the 100 ft.c. 16L : 8D the RT and HR rhythms remained stable and circadian throughout. When the light intensity was decreased to 15 ft.c. the periodicity of the HR rhythm was significantly decreased and this rhythm showed marked instability. In contrast the period of the RT rhythm did not change but a consistent phase delay occurred due to a delay in the lights-on associated rise in RT. These divergent effects on these two rhythms in internal desynchronization and performance decrement during the 15 ft.c. exposure. The data emphasize the need for establishing accurately the minimal lighting requirements for the maintenance of circadian rhythms of humans in confined environments.

Neural Comput 2003 Mar;15(3):509-38

Synchronization in networks of excitatory and inhibitory neurons with sparse, random connectivity.

Borgers C, Kopell N.

Department of Mathematics, Tufts University, Medford, MA 02155, U.S.A. chritopher.borgers@tufts.edu

In model networks of E-cells and I-cells (excitatory and inhibitory neurons, respectively), synchronous rhythmic spiking often comes about from the interplay between the two cell groups: the E-cells synchronize the I-cells and vice versa. Under ideal conditions-homogeneity in relevant network parameters and all-to-all connectivity, for instance-this mechanism can yield perfect synchronization. We find that approximate, imperfect synchronization is possible even with very sparse, random connectivity. The crucial quantity is the expected number of inputs per cell. As long as it is large enough (more precisely, as long as the variance of the total number of synaptic inputs per cell is small enough), tight synchronization is possible. The desynchronizing effect of random connectivity can be reduced by strengthening the E --> I synapses. More surprising, it cannot be reduced by strengthening the I --> E synapses. However, the decay time constant of inhibition plays an important role. Faster decay yields tighter synchrony. In particular, in models in which the inhibitory synapses are assumed to be instantaneous, the effects of sparse, random connectivity cannot be seen.

Philos Trans R Soc Lond B Biol Sci 2002 Dec 29;357(1428):1659-73

Thalamic circuitry and thalamocortical synchrony.

Jones EG.

Center for Neuroscience, University of California, Davis, Davis, CA 95616, USA. ejones@ucdavis.edu

The corticothalamic system has an important role in synchronizing the activities of thalamic and cortical neurons. Numerically, its synapses dominate the inputs to relay cells and to the gamma-amino butyric acid (GABA)ergic cells of the reticular nucleus (RTN). The capacity of relay neurons to operate in different voltage-dependent functional modes determines that the inputs from the cortex have the capacity directly to excite the relay cells, or indirectly to inhibit them via the RTN, serving to synchronize high- or low-frequency oscillatory activity respectively in the thalamocorticothalamic network. Differences in the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) subunit composition of receptors at synapses formed by branches of the same corticothalamic axon in the RTN and dorsal thalamus are an important element in the capacity of the cortex to synchronize low-frequency oscillations in the network. Interactions of focused corticothalamic axons arising from layer VI cortical cells and diffuse corticothalamic axons arising from layer V cortical cells, with the specifically projecting core relay cells and diffusely projecting matrix cells of the dorsal thalamus, form a substrate for synchronization of widespread populations of cortical and thalamic cells during high-frequency oscillations that underlie discrete conscious events.

Nat Neurosci 2003 Jun;6(6):593-9

Synchrony-dependent propagation of firing rate in iteratively constructed networks in vitro.

Reyes AD.

Center for Neural Science, New York University, 4 Washington Place, New York, New York 10003, USA. reyes@cns.nyu.edu

The precise role of synchronous neuronal firing in signal encoding remains unclear. To examine what kinds of signals can be carried by synchrony, I reproduced a multilayer feedforward network of neurons in an in vitro slice preparation of rat cortex using an iterative procedure. When constant and time-varying frequency signals were delivered to the network, the firing of neurons in successive layers became progressively more synchronous. Notably, synchrony in the in vitro network developed even with uncorrelated input, persisted under a wide range of physiological conditions and was crucial for the stable propagation of rate signals. The firing rate was represented by a classical rate code in the initial layers, but switched to a synchrony-based code in the deeper layers.

Neuron 2003 Apr 10;38(1):115-25

Synchrony between Neurons with Similar Muscle Fields in Monkey Motor Cortex.

Jackson A, Gee VJ, Baker SN, Lemon RN.

Sobell Department of Motor Neuroscience and Movement Disorders, Institute of Neurology, UCL, WC1N 3BG, London, United Kingdom

Synchronous firing of motor cortex cells exhibiting postspike facilitation (PSF) or suppression (PSS) of hand muscle EMG was examined to investigate the relationship between synchrony and output connectivity. Recordings were made in macaque monkeys performing a precision grip task. Synchronization was assessed with cross-correlation histograms of the activity from 144 pairs of simultaneously recorded neurons, while spike-triggered averages of EMG defined the muscle field for each cell. Cell pairs with similar muscle fields showed greater synchronization than pairs with nonoverlapping fields. Furthermore, cells with opposing effects in the same muscles exhibited negative synchronization. We conclude that synchrony in motor cortex engages networks of neurons directly controlling the same muscle set, while inhibitory connections exist between neuronal populations with opposing output effects.
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Neuropsychopharmacology 2003 May;28(5):857-64

Norepinephrine but not Serotonin Reuptake Inhibitors Enhance Theta and Gamma Activity of the Septo-Hippocampal System.

Hajos M, Hoffmann WE, Robinson DD, Yu JH, Hajos-Korcsok E.

1Neurobiology, Pharmacia Corporation, Kalamazoo, MI, USA.

Current neurobiological concepts attribute a central role of the hippocampal formation in cognitive and affective processes. Recent studies indicate that the hippocampus is affected in human depression, and antidepressant drugs induce hippocampal adaptive changes that are thought to be associated with their therapeutic action. In the present study, we investigated the action of various antidepressant drugs on the activity of the septo-hippocampal system, its oscillatory activity in particular. The acute effects of the norepinephrine (NE) reuptake inhibitors reboxetine and desipramine, and the selective serotonin reuptake inhibitor fluvoxamine were evaluated. Extracellular single-unit recordings were performed from the medial septum/diagonal band of Broca (MS/DBv), with simultaneous hippocampal EEG recordings of anesthetized rats. Systemic administration of reboxetine synchronized hippocampal EEG, resulting in a significant increase in power at theta frequency, and an increase in frequency and power of gamma-wave activity. Parallel to EEG synchrony, reboxetine induced or enhanced theta oscillation of MS/DBv neurons. Oscillatory frequencies of MS/DBv neurons were identical, and phase locked to the corresponding hippocamapal theta frequencies. Under the same experimental conditions, reboxetine induced a two-fold increase in extracellular NE (but not serotonin) levels in the hippocampus as revealed by microdialysis. Desipramine, but not the serotonin reuptake inhibitor fluvoxamine, evoked responses similar to those of reboxetine regarding septo-hippocampal theta activity. The present findings indicate that even though both NE and serotonin reuptake inhibitors are clinically effective antidepressant drugs, their action on the septo-hippocampal oscillatory behavior is different. It is presumed that selective NE reuptake inhibitors could modulate various cognitive processes associated with hippocampal oscillatory activity.Neuropsychopharmacology (2003) 28, 857-864,

Phys Rev Lett 2003 Feb 28;90(8):088101

Synchronization tomography: a method for three-dimensional localization of phase synchronized neuronal populations in the human brain using magnetoencephalography.

Tass PA, Fieseler T, Dammers J, Dolan K, Morosan P, Majtanik M, Boers F, Muren A, Zilles K, Fink GR.

Institute of Medicine, Research Center Julich, 52425 Julich, Germany.

We present a noninvasive technique which allows the anatomical localization of phase synchronized neuronal populations in the human brain with magnetoencephalography. We study phase synchronization between the reconstructed current source density (CSD) of different brain areas as well as between the CSD and muscular activity. We asked four subjects to tap their fingers in synchrony with a rhythmic tone, and to continue tapping at the same rate after the tone was switched off. The phase synchronization behavior of brain areas relevant for movement coordination, inner voice, and time estimation changes drastically when the transition to internal pacing occurs, while their averaged amplitudes remain unchanged. Information of this kind cannot be derived with standard neuroimaging techniques like functional magnetic resonance imaging or positron emission tomography.

Cell Cycle 2003 Jan-Feb;2(1):42-5

Synchrony in human, mouse and bacterial cell cultures a comparison.

Helmstetter CE, Thornton M, Romero A, Eward LK.

Correspondence to: Charles E. Helmstetter; Department of Biological Sciences; Florida Institute of Technology; Melbourne, Florida 32901 USA; Tel.: 321.674.8575; Fax: 321.674.7238.

Growth characteristics of synchronous human MOLT-4, human U-937 and mouse L1210 cultures produced with a new minimally-disturbing technology were compared to each other and to synchronous Escherichia coli B/r. Based on measurements of cell concentrations during synchronous growth, synchrony persisted in similar fashion for all cells. Cell size and DNA distributions in the mammalian cultures also progressed synchronously and reproducibly for multiple cell cycles. The results demonstrate that unambiguous multi-cycle synchrony, critical for verifying the absence of significant growth imbalances induced by the synchronization procedure, is feasible with these cell lines, and possibly others.

J Neurophysiol 2003 Apr 17;

Features of Neuronal Synchrony in Mouse Visual Cortex.

Nase G, Singer W, Monyer H, Engel AK.

Neurophysiologie, Max-Planck-Institut fuer Hirnforschung, Frankfurt, Germany.

Synchronization of neuronal discharges has been hypothesized to play a role in defining cell assemblies representing particular constellations of stimulus features. In many systems and species, synchronization is accompanied by an oscillatory response modulation at frequencies in the gamma-band (>30Hz). The cellular mechanisms underlying these phenomena of synchronization and oscillatory patterning have been studied mainly in vitro due to the difficulty in designing a direct in vivo assay. With the prospect of utilizing conditional genetic manipulations of cortical network components, our objective was to test whether the mouse would meet the criteria to provide a model system for the study of gamma-band synchrony. Multi-unit and local field potential recordings were made from the primary visual cortex of anesthetized C57BL/6J mice. Neuronal responses evoked by moving gratings, bars and random dot patterns were analyzed with respect to neuronal synchrony and temporal patterning. Oscillations at gamma frequencies were readily evoked with all types of stimuli used. Oscillation and synchronization strength were largest for gratings and decreased when the noise level was increased in random-dot patterns. The center peak width of cross-correlograms was smallest for bars and increased with noise, yielding a significant difference between coherent random dot patterns versus patterns with >70% noise. Field potential analysis typically revealed increases of power in the gamma-band during response periods. Our findings are compatible with a role for neuronal synchrony in mediating perceptual binding and suggest the usefulness of the mouse model for testing hypotheses concerning both the mechanisms and the functional role of temporal patterning.

Brain Lang 2003 May;85(2):297-312

Cortical operational synchrony during audio-visual speech integration.

Fingelkurts AA, Fingelkurts AA, Krause CM, Mottonen R, Sams M.

Human Brain Research Group, Human Physiology Department, Moscow State University, 119899, Moscow, Russian Federation

Information from different sensory modalities is processed in different cortical regions. However, our daily perception is based on the overall impression resulting from the integration of information from multiple sensory modalities. At present it is not known how the human brain integrates information from different modalities into a unified percept. Using a robust phenomenon known as the McGurk effect it was shown in the present study that audio-visual synthesis takes place within a distributed and dynamic cortical networks with emergent properties. Various cortical sites within these networks interact with each other by means of so-called operational synchrony (). The temporal synchronization of cortical operations processing unimodal stimuli at different cortical sites reveals the importance of the temporal features of auditory and visual stimuli for audio-visual speech integration.

J Comput Neurosci 2003 May-Jun;14(3):283-309

Dynamics of spiking neurons connected by both inhibitory and electrical coupling.

Lewis TJ, Rinzel J.

Center for Neural Science and Courant Institute for Mathematical Science, New York University, 4 Washington Place, Rm 809, NY 10003, USA. tim.lewis@nyu.edu

We study the dynamics of a pair of intrinsically oscillating leaky integrate-and-fire neurons (identical and noise-free) connected by combinations of electrical and inhibitory coupling. We use the theory of weakly coupled oscillators to examine how synchronization patterns are influenced by cellular properties (intrinsic frequency and the strength of spikes) and coupling parameters (speed of synapses and coupling strengths). We find that, when inhibitory synapses are fast and the electrotonic effect of the suprathreshold portion of the spike is large, increasing the strength of weak electrical coupling promotes synchrony. Conversely, when inhibitory synapses are slow and the electrotonic effect of the suprathreshold portion of the spike is small, increasing the strength of weak electrical coupling promotes antisynchrony (see Fig. 10). Furthermore, our results indicate that, given a fixed total coupling strength, either electrical coupling alone or inhibition alone is better at enhancing neural synchrony than a combination of electrical and inhibitory coupling. We also show that these results extend to moderate coupling strengths.
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J Exp Psychol Hum Percept Perform 2003 Apr;29(2):290-309

Phase attraction in sensorimotor synchronization with auditory sequences: effects of single and periodic distractors on synchronization accuracy.

Repp BH.

Haskins Laboratories, New Haven, Connecticut 06511-6695, USA. repp@haskins.yale.edu

Four experiments showed that both single and periodic distractor tones affected the timing of finger taps produced in synchrony with an isochronous auditory target sequence. Single distractors had only small effects, but periodic distractors occurring at various fixed or changing phase relationships exerted strong phase attraction. The attraction was asymmetric, being stronger when distractors preceded target tones than when they lagged behind. A large pitch difference between target and distractor tones (20 vs. 3 semitones) did not reduce phase attraction substantially, although in the case of continuously changing phase relationships it did prevent complete capture of the taps by the distractors. The results support the hypothesis that phase attraction is an automatic process that is sensitive primarily to event onsets.

Brain Lang 2003 May;85(2):211-21

Neural basis for sentence comprehension deficits in frontotemporal dementia.

Cooke A, DeVita C, Gee J, Alsop D, Detre J, Chen W, Grossman M.

Department of Neurology-2 Gibson, University of Pennsylvania Medical Center, 3400 Spruce Street, 19104-4283, Philadelphia, PA, USA

Many patients with frontotemporal dementia (FTD) have impaired sentence comprehension. However, the pattern of comprehension difficulty appears to vary depending on the clinical subgroup. The purpose of this study was to elucidate the neural basis for these deficits in FTD. We studied patients with two different presentations: Three patients with Progressive Non-Fluent Ahasia (PNFA), and five non-aphasic patients with a dysexecutive and social impairment (EXEC). The FTD patient subgroups were compared to a cohort of 11 healthy seniors with intact sentence comprehension. We monitored regional cerebral activity with blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI) while subjects read sentences featuring both a grammatically complex object-relative center-embedded clause and a long linkage between the head noun phrase (NP) and the gap where the NP is interpreted in the center-embedded clause. Subjects decided whether the agent of the action is a male or a female. Healthy seniors activated both ventral portions of inferior frontal cortex (vIFC) and dorsal portions of IFC (dIFC) in the left hemisphere, often associated with grammatical and working memory components of these sentences, respectively. PNFA patients differed from healthy controls since they have reduced activation of left vIFC, while EXEC patients have less recruitment of left dIFC. We conclude that FTD subgroups have distinct patterns of sentence comprehension difficulty in part because of selective interruptions of a large-scale neural network for sentence processing.

Brain Res Cogn Brain Res 2003 Jun;17(1):56-67

Shared and dissociated cortical regions for object and letter processing.

Joseph JE, Gathers AD, Piper GA.

Department of Anatomy and Neurobiology, University of Kentucky Medical Center, 800 Rose Street, Davis-Mills Building, Room 308, 40536-0098, Lexington, KY, USA

The present study determined the extent to which object and letter recognition recruit similar or dissociated neural resources. Participants passively viewed and silently named line drawings of objects, single letters, and visual noise patterns and centrally fixated an asterisk. We used whole-brain functional MRI and a very conservative approach to hypothesis testing that distinguished among brain regions that were selectively activated by different experimental conditions and those that were conjointly activated. The left fusiform gyrus (BA 19 & 37) and left inferior frontal cortex BA(44/6) showed a greater degree of conjoined activation for objects and letters than selective activation for either category, whereas left inferior parietal cortex (BA 40) and the left insula showed a strong letter-selective response. Equal recruitment of left fusiform and inferior frontal regions by objects and letters reflects similar demands on cognitive processing by these two categories and argues against category-specific modules in these regions. However, cortical systems for object and letter processing are not completely shared given the exclusive activation of left inferior parietal cortex by letters.

J Neurophysiol 2003 May 15;

Synchrony levels during Evoked Seizure-Like Bursts in Mouse Neocortical Slices.

Van Drongelen W, Koch H, Marcuccilli C, Pena F, Ramirez JM.

Pediatrics, The University of Chicago, Chicago, IL, USA; Neurology, The University of Chicago, Chicago, IL, USA.

Slices (n = 45) from the somatosensory cortex of mouse (P8-13) generate spontaneous bursts of activity (0.10 +/-0.05 Hz) that were recorded extracellularly. Multi-unit action potential (AP) activity was integrated and used as an index of population activity. In this experimental model, seizure-like activity (SLA) was evoked with bicuculline (5-10 micro M) or N-methyl-D-aspartate (NMDA, 5 micro M). SLA was an episode with repetitive bursting at a frequency of 0.50 +/-0.06 Hz. To evaluate whether SLA was associated with a change in synchrony, we obtained simultaneous intracellular and extracellular recordings (n = 40) and quantified the relationship between individual cells and the surrounding population of neurons. During the SLA there was an increase in population activity and bursting activity was observed in neurons and areas that were previously silent. We defined synchrony as cellular activity that is consistently locked with the population bursts. Signal averaging techniques were used to determine this component. To quantitatively assess change in synchronous activity at SLA onset, we estimated the entropy of the single cell spike trains and subdivided this measure into network burst related information and noise-related entropy. The burst related information was not significantly altered at the onset of NMDA evoked SLA and slightly increased when evoked with bicuculline. The signal-to-noise ratio determined from the entropy estimates showed a significant decrease (instead of an expected increase) during SLA. We conclude that the increased population activity during the SLA is due to recruitment of neurons rather than increased synchrony of each of the individual elements.

International Journal of Bifurcation and Chaos, Vol. 10, No. 10 (2000) 2307-2322

CHARACTERISTICS OF THE SYNCHRONIZATION OF BRAIN ACTIVITY IMPOSED BY FINITE CONDUCTION VELOCITIES OF AXONS

WALTER J. FREEMAN
Division of Neurobiology LSA 129, Department of Molecular & Cell Biology, University of California, Berkeley CA 94720-3200, USA
The electrical activity of neurons in brains fluctuates erratically both in terms of pulse trains of single neurons and the dendritic currents of populations of neurons. Obviously the neurons interact with one another in the production of intelligent behavior, so it is reasonable to expect to find evidence for varying degrees of synchronization of their pulse trains and dendritic currents in relation to behavior. However, synaptic communication between neurons depends on propagation of action potentials between neurons, often with appreciable distances between them, and the transmission delays are not compatible with synchronization in any simple way. Evidence is on hand showing that the principal form of synchrony is by establishment of a low degree of covariance among very large numbers of otherwise autonomous neurons, which allows for rapid state transitions of neural populations between successive chaotic basins of attraction along itinerant trajectories. The small fraction of covariant activity is extracted by spatial integration upon axonal transmission over divergent-convergent pathways, through which a remarkable improvement in signal-to-noise ratio is achieved. The raw traces of local activity show little evidence for synchrony, other than zero-lag correlation, which appears to be largely a statistical artifact. Brains rely less on tight phase-locking of small numbers of periodically firing neurons and more on low degrees of cooperativity achieved by order parameters influencing very large numbers of neurons. Brains appear to be indifferent to and undisturbed by widely varying time and phase relations between individual neurons and even large semi-autonomous areas of cortex comprising their mesoscopic neural masses.

Exp Brain Res 2003 May 9;

Ia Afferent input alters the recruitment thresholds and firing rates of single human motor units.

Grande G, Cafarelli E.

Kinesiology and Health Science, Faculty of Pure and Applied Science, York University, Toronto, Canada.

Vibration of the patellar tendon recruits motor units in the knee extensors via excitation of muscle spindles and subsequent Ia afferent input to the alpha-motoneuron pool. Our first purpose was to determine if the recruitment threshold and firing rate of the same motor unit differed when recruited involuntarily via reflex or voluntarily via descending spinal pathways. Although Ia input is excitatory to the alpha-motoneuron pool, it has also been shown paradoxically to inhibit itself. Our second purpose was to determine if vibration of the patellar tendon during a voluntary knee extension causes a change in the firing rate of already recruited motor units. In the first protocol, 10 subjects voluntarily reproduced the same isometric force profile of the knee extensors that was elicited by vibration of the patellar tendon. Single motor unit recordings from the vastus lateralis (VL) were obtained with tungsten microelectrodes and unitary behaviour was examined during both reflex and voluntary knee extensions. Recordings from 135 single motor units showed that both recruitment thresholds and firing rates were lower during reflex contractions. In the second protocol, 7 subjects maintained a voluntary knee extension at 30 N for approximately 40-45 s. Three bursts of patellar tendon vibration were superimposed at regular intervals throughout the contraction and changes in the firing rate of already recruited motor units were examined. A total of 35 motor units were recorded and each burst of superimposed vibration caused a momentary reduction in the firing rates and recruitment of additional units. Our data provide evidence that Ia input modulates the recruitment thresholds and firing rates of motor units providing more flexibility within the neuromuscular system to grade force at low levels of force production.

Exp Brain Res 2003 Jan;148(2):238-46

Processing of temporal information and the basal ganglia: new evidence from fMRI.

Nenadic I, Gaser C, Volz HP, Rammsayer T, Hager F, Sauer H.

Department of Psychiatry, Friedrich-Schiller-University of Jena, Philosophenweg 3, 07740 Jena, Germany, igor.nenadic@uni-jena.de

Temporal information processing is a fundamental brain function, which might include central timekeeping mechanisms independent of sensory modality. Psychopharmacological and patient studies suggest a crucial role of the basal ganglia in time estimation. In this study, functional magnetic resonance imaging (fMRI) was applied in 15 healthy right-handed male subjects performing an auditory time estimation task (duration discrimination of tone pairs in the range of 1,000-1,400 ms) and frequency discriminations (tone pairs differing in pitch, around 1,000 Hz) as an active control task. Task difficulty was constantly modulated by an adaptive algorithm (weighted up-down method) reacting on individual performance. Time estimation (vs rest condition) elicited a distinct pattern of cerebral activity, including the right medial and both left and right dorsolateral prefrontal cortices (DLPFC), thalamus, basal ganglia (caudate nucleus and putamen), left anterior cingulate cortex, and superior temporal auditory areas. Most activations showed lateralisation to the right hemisphere and were similar in the frequency discrimination task. Comparing time and frequency tasks, we isolated activation in the right putamen restricted to time estimation only. This result supports the notion of central processing of temporal information associated with basal ganglia activity. Temporal information processing in the brain might thus be a distributed process of interaction between modality-dependent sensory cortical function, the putamen (with a timing-specific function), and additional prefrontal cortical systems related to attention and memory. Further investigations are needed to delineate the differential contributions of the striatum and other areas to timing.

J Neurophysiol 2003 Jan;89(1):460-71

Modulation of cortical activity during different imitative behaviors.

Koski L, Iacoboni M, Dubeau MC, Woods RP, Mazziotta JC.

Ahmanson-Lovelace Brain Mapping Center, Neuropsychiatric Institute, UCLA School of Medicine, Los Angeles, California 90095.

Imitation is a basic form of motor learning during development. We have a preference to imitate the actions of others as if looking in a mirror (specular imitation: i.e., when the actor moves the left hand, the imitator moves the right hand) rather than with the anatomically congruent hand (anatomic imitation: i.e., actor and imitator both moving the right hand). We hypothesized that this preference reflects changes in activity in previously described frontoparietal cortical areas involved in directly matching observed and executed actions (mirror neuron areas). We used functional magnetic resonance imaging to study brain activity in normal volunteers imitating left and right hand movements with their right hand. Bilateral inferior frontal and right posterior parietal cortex were more active during specular imitation compared with anatomic imitation and control motor tasks. Furthermore this same pattern of activity was also observed in the rostral part of the supplementary motor area (SMA-proper) of the right hemisphere. These findings suggest that the degree of involvement of frontoparietal mirror areas in imitation depends on the nature of the imitative behavior, ruling out a linguistic mediation of these areas in imitation. Moreover, activity in the SMA appears to be tightly coupled to frontoparietal mirror areas when subjects copy the actions of others.

Proc Natl Acad Sci U S A 2003 Feb 4;100(3):1370-4

Contrasting roles of axonal (pyramidal cell) and dendritic (interneuron) electrical coupling in the generation of neuronal network oscillations.

Traub RD, Pais I, Bibbig A, LeBeau FE, Buhl EH, Hormuzdi SG, Monyer H, Whittington MA.

Department of Physiology and Pharmacology, State University of New York Downstate Medical Center, 450 Clarkson Avenue, Box 31, Brooklyn, NY 11203, USA. roger.traub@downstate.edu

Electrical coupling between pyramidal cell axons, and between interneuron dendrites, have both been described in the hippocampus. What are the functional roles of the two types of coupling? Interneuron gap junctions enhance synchrony of gamma oscillations (25-70 Hz) in isolated interneuron networks and also in networks containing both interneurons and principal cells, as shown in mice with a knockout of the neuronal (primarily interneuronal) connexin36. We have recently shown that pharmacological gap junction blockade abolishes kainate-induced gamma oscillations in connexin36 knockout mice; without such gap junction blockade, gamma oscillations do occur in the knockout mice, albeit at reduced power compared with wild-type mice. As interneuronal dendritic electrical coupling is almost absent in the knockout mice, these pharmacological data indicate a role of axonal electrical coupling in generating the gamma oscillations. We construct a network model of an experimental gamma oscillation, known to be regulated by both types of electrical coupling. In our model, axonal electrical coupling is required for the gamma oscillation to occur at all; interneuron dendritic gap junctions exert a modulatory effect

Nature 2003 Jan 23;421(6921):366-70

Neuronal synchrony does not correlate with motion coherence in cortical area MT.

Thiele A, Stoner G.

Salk Institute for Biological Studies, La Jolla, California 92037, USA.

Natural visual scenes are cluttered with multiple objects whose individual features must somehow be selectively linked (or 'bound') if perception is to coincide with reality. Recent neurophysiological evidence supports a 'binding-by-synchrony' hypothesis: neurons excited by features of the same object fire synchronously, while neurons excited by features of different objects do not. Moving plaid patterns offer a straightforward means to test this idea. By appropriate manipulations of apparent transparency, the component gratings of a plaid pattern can be seen as parts of a single coherently moving surface or as two non-coherently moving surfaces. We examined directional tuning and synchrony of area-MT neurons in awake, fixating primates in response to perceptually coherent and non-coherent plaid patterns. Here we show that directional tuning correlated highly with perceptual coherence, which is consistent with an earlier study. Although we found stimulus-dependent synchrony, coherent plaids elicited significantly less synchrony than did non-coherent plaids. Our data therefore do not support the binding-by-synchrony hypothesis as applied to this class of motion stimuli in area MT.

J Acoust Soc Am 2003 Jan;113(1):462-7

Effect of amplitude modulation coherence for masked speech signals filtered into narrow bands.

Buss E, Wall JW 3rd, Grose JH.

Department of Otolaryngology/Head and Neck Surgery, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27599, USA. ebuss@med.unc.edu

Introduction of masker amplitude modulation (AM) can improve signal detection in a number of paradigms. In some cases this advantage depends on the coherence of modulation across a relatively wide frequency range. In the experiments described below, observers were asked to identify masked spondee words produced by a single male talker. The target spondees and masking noise were filtered into nine narrow bands, and the coherence of AM of either the speech signal or noise masker was manipulated. Inherent modulation of the masker bands was manipulated via assignment of real and imaginary values to the associated components of each band in the frequency domain, and AM of speech bands was achieved via multiplication with envelopes extracted from these maskers. Responses were based on two alternatives, four alternatives, or open response sets. The effect of masker AM coherence was highly dependent upon the size of the response set: coherent AM was associated with better thresholds in a two-alternative response set, but poorer thresholds in an open response set. Results with AM speech did not depend critically upon the across-frequency temporal synchrony of AM imposed on the speech material.

Hemisphere specialization as an aid in early infancy.

Burnand G.

burn@globalnet.co.uk

In order that different directions of attention can be organized, they have to be labeled and assessed. A statement of a general problem can be regarded as a label for a general direction of attention. Hope about it, as the perceived probability of sufficient success, on the basis of work done, can be regarded as an assessment. It can be argued that a young infant meets an impasse arising from the work on 2 incompatible general problems, (1) that of raising hope of certainty about the environment (linked to the arousal system because repeated stimulation has less effect), and (2) that of raising hope of producing effects (linked to the activation system because here some effect must be produced before activity can cease). A certainty-right hypothesis, that the right hemisphere deals with the certainty problem and the left deals with the producing-effects problem, and hence keeps work on the two problems apart in early infancy while the corpus callosum is undeveloped, and that a matching specialization continues in later life, is supported.
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Hermaphrodite finch hints genes mould brain
Sex chromosomes split personality in bird possessing testis and ovary.
25 March 2003
JOHN WHITFIELD

The half-half finch: male on one side, female on the other

A half-male, half-female bird has added to evidence that genes - not only hormones - underlie the differences between male and female brains.

The cells on the right half of the bird's body contained male sex chromosomes, those on the left, female. The zebra finch had one testis and one ovary; its plumage was bright on its right half, and drab on its left.

It also had a split personality. When ornithologist John Wingfield and his colleagues looked at the bird's brain, they saw that it, too, was divided into male and female sides.

The areas that control singing were bigger on the male side. Male finches court mates with loud and complex songs; females are quieter.

It had been thought that sex differences in the brain were caused by hormones released by the gonads, and were not due to the nerve cells themselves. But both halves of the brain would have received the same chemical signals from the gonads, showing that the different genetic make-up of the brain's two halves must also have had an effect.

The divided bird sang a male's song, and mated a female finch that then laid infertile eggs. The researchers put down the bird when it was almost two years old.

The bizarre zebra finch (Taeniopygia guttata) was born in a lab at Rockefeller University, New York, possibly from a cell containing both male and female chromosomes that was fertilized by two sperm.

Wingfield, who works at the University of Washington, Seattle, was baffled when he first saw the animal - it seemed to change sex before his eyes as it turned. "It was split straight down the middle," he says.

References
Agate, R. J. et al. Neural, not gonadal, origin of brain sex differences in a gynandromorphic finch. Proceedings of the National Academy of Sciences, (2003).

Neuron 2002 Dec 19;36(6):1221-31

The role of medial temporal lobe structures in implicit learning: an event-related FMRI study.

Rose M, Haider H, Weiller C, Buchel C.

Cognitive Neuroscience Laboratory, Department of Neurology, University of Hamburg Medical School, D-20246, Hamburg, Germany. rose@uke.uni-hamburg.de

The medial temporal lobe (MTL) has been associated with declarative learning of flexible relational rules and the basal ganglia with implicit learning of stimulus-response mappings. It remains an open question of whether MTL or basal ganglia are involved when learning flexible relational contingencies without awareness. We studied learning of an explicit stimulus-response association with fMRI. Embedded in this explicit task was a hidden structure that was learnt implicitly. Implicit learning of the sequential regularities of the "hidden rule" activated the ventral perirhinal cortex, within the MTL, whereas learning the fixed stimulus-response associations activated the basal ganglia, indicating that the function of the MTL and the basal ganglia depends on the learned material and not necessarily on the participants' awareness.

Neuroreport 2002 Dec 20;13(18):2475-2481

Alteration of functional neuroanatomy of simple object memory in medial temporal lobe epilepsy patients.

Kang E, Nam H, Lee DS, Lee SK, Lee K, Park SH, Lee JS, Chung JK, Lee MC.

Institute of Radiation Medicine, Seoul National University Medical Research Center Departments of Nuclear Medicine.

Using H O PET, we examined the neuroanatomy associated with a simple form of episodic memory in patients with right or left medial temporal lobe epilepsy and normal healthy controls. When line drawings of common objects were memorized and tested after a 30 min delay, no behavioral difference was found between the patient groups and the controls. However, the patients with epilepsy showed greater cortical activations than the control group on the side ipsilateral to the epileptic focus. rCBF in the anterior thalamic region was enhanced in patients relative to the control group. The results showed that long-term dysfunction of the medial temporal lobe might reinforce alternative memory pathways and recruit a distributed cortical network ipsilateral to their epilepsy focus.(2)

Neuron 2003 Jan 9;37(1):171-80

Recognition memory and the human hippocampus.

Manns JR, Hopkins RO, Reed JM, Kitchener EG, Squire LR.

University of California, San Diego, 92093, La Jolla, CA, USA

The capacity for declarative memory depends on the hippocampal region and adjacent cortex within the medial temporal lobe. One of the most widely studied examples of declarative memory is the capacity to recognize recently encountered material as familiar, but uncertainty remains about whether intact recognition memory depends on the hippocampal region itself and, if so, what the nature of the hippocampal contribution might be. Seven patients with bilateral damage thought to be limited primarily to the hippocampal region were impaired on three standard tests of recognition memory. In addition, the patients were impaired to a similar extent at Remembering and Knowing, measures of the two processes thought to support recognition performance: the ability to remember the learning episode (episodic recollection) and the capacity for judging items as familiar (familiarity).

Rev Neurosci 2002;13(4):299-312

The interaction of rhinal cortex and hippocampus in human declarative memory formation.

Fell J, Klaver P, Elger CE, Fernandez G.

Department of Epileptology, University of Bonn, Bonn, Germany. juergen.fell@ukb.uni-bonn.de

Human declarative memory formation crucially depends on processes within the medial temporal lobe (MTL). These processes can be monitored in real-time by recordings from depth electrodes implanted in the MTL of patients with epilepsy who undergo presurgical evaluation. In our studies, patients performed a word memorization task during depth EEG recording. Afterwards, the difference between event-related potentials (ERPs) corresponding to subsequently remembered versus forgotten words was analyzed. These kind of studies revealed that successful memory encoding is characterized by an early process generated by the rhinal cortex within 300 ms following stimulus onset. This rhinal process precedes a hippocampal process, which starts about 200 ms later. Further investigation revealed that the rhinal process seems to be a correlate of semantic preprocessing which supports memory formation, whereas the hippocampal process appears to be a correlate of an exclusively mnemonic operation. These studies yielded only indirect evidence for an interaction of rhinal cortex and hippocampus. Direct evidence for a memory related cooperation between both structures, however, has been found in a study analyzing so called gamma activity, EEG oscillations of around 40 Hz. This investigation showed that successful as opposed to unsuccessful memory formation is accompanied by an initial enhancement of rhinal-hippocampal phase synchronization, which is followed by a later desynchronization. Present knowledge about the function of phase synchronized gamma activity suggests that this phase coupling and decoupling initiates and later terminates communication between the two MTL structures. Phase synchronized rhinal-hippocampal gamma activity may, moreover, accomplish Hebbian synaptic modifications and thus provide an initial step of declarative memory formation on the synaptic level.

Science 2003 Jan 24;299(5606):577-80

Dynamics of the hippocampus during encoding and retrieval of face-name pairs.

Zeineh MM, Engel SA, Thompson PM, Bookheimer SY.

Ahmanson-Lovelace Brain Mapping Center, UCLA School of Medicine, 660 Charles Young Drive South, Los Angeles, CA 90095-7085, USA.

The medial temporal lobe (MTL) is critical in forming new memories, but how subregions within the MTL carry out encoding and retrieval processes in humans is unknown. Using new high-resolution functional magnetic resonance imaging (fMRI) acquisition and analysis methods, we identified mnemonic properties of different subregions within the hippocampal circuitry as human subjects learned to associate names with faces. The cornu ammonis (CA) fields 2 and 3 and the dentate gyrus were active relative to baseline only during encoding, and this activity decreased as associations were learned. Activity in the subiculum showed the same temporal decline, but primarily during retrieval. Our results demonstrate that subdivisions within the hippocampus make distinct contributions to new memory formation.

J Neurophysiol 2002 Sep;88(3):1433-50

Sound repetition rate in the human auditory pathway: representations in the waveshape and amplitude of fMRI activation.

Harms MP, Melcher JR.

Eaton-Peabody Laboratory, Massachusetts Eye and Ear Infirmary, Boston 02114, USA. mharms@epl.meei.harvard.edu

Sound repetition rate plays an important role in stream segregation, temporal pattern recognition, and the perception of successive sounds as either distinct or fused. This study was aimed at elucidating the neural coding of repetition rate and its perceptual correlates. We investigated the representations of rate in the auditory pathway of human listeners using functional magnetic resonance imaging (fMRI), an indicator of population neural activity. Stimuli were trains of noise bursts presented at rates ranging from low (1-2/s; each burst is perceptually distinct) to high (35/s; individual bursts ar

NeuroScience References / Further Reading

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