CiteULike: Group: UC Berkeley Spring 2008 Cog Neuro Readings - library [37 articles]

Neurometabolic coupling in cerebral cortex reflects synaptic more than spiking activity.

A Viswanathan — 2008-01-30T07:31:12-00:00

Nature Neuroscience, Vol. 10, No. 10. (October 2007), pp. 1308-1312.

In noninvasive neuroimaging, neural activity is inferred from local fluctuations in deoxyhemoglobin. A fundamental question of functional magnetic resonance imaging (fMRI) is whether the inferred neural activity is driven primarily by synaptic or spiking activity. The answer is critical for the interpretation of the blood oxygen level–dependent (BOLD) signal in fMRI. Here, we have used well-established visual-system circuitry to create a stimulus that elicits synaptic activity without associated spike discharge. In colocalized recordings of neural and metabolic activity in cat primary visual cortex, we observed strong coupling between local field potentials (LFPs) and changes in tissue oxygen concentration in the absence of spikes. These results imply that the BOLD signal is more closely coupled to synaptic activity.

Transcranial magnetic stimulation elicits coupled neural and hemodynamic consequences.

EA Allen — 2008-01-30T07:39:11-00:00

Science, Vol. 317, No. 5846. (28 September 2007), pp. 1918-1921.

Transcranial magnetic stimulation (TMS) is an increasingly common technique used to selectively modify neural processing. However, application of TMS is limited by uncertainty concerning its physiological effects. We applied TMS to the cat visual cortex and evaluated the neural and hemodynamic consequences. Short TMS pulse trains elicited initial activation (~1 minute) and prolonged suppression (5 to 10 minutes) of neural responses. Furthermore, TMS disrupted the temporal structure of activity by altering phase relationships between neural signals. Despite the complexity of this response, neural changes were faithfully reflected in hemodynamic signals; quantitative coupling was present over a range of stimulation parameters. These results demonstrate long-lasting neural responses to TMS and support the use of hemodynamic-based neuroimaging to effectively monitor these changes over time.

Adaptation: from single cells to BOLD signals

B Krekelberg — 2008-01-30T07:43:13-00:00

Trends in Neuroscience, Vol. 29, No. 5. (May 2006), pp. 250-256.

Functional magnetic resonance imaging adaptation (fMRIa) is an increasingly popular method that aims to provide insight into the functional properties of subpopulations of neurons within an imaging voxel. The technique relies on the assumption that neural adaptation reduces activity when two successive stimuli activate the same subpopulation but not when they stimulate different subpopulations. Here, we assess the validity of fMRIa by comparing single-cell recordings with functional imaging of orientation, motion and face processing. We find that fMRIa provides novel insight into neural representations in the human brain. However, network responses in general and adaptation in particular are more complex than is often assumed, and an unequivocal interpretation of fMRIa results can be achieved only with great care.

Using FMRI brain activation to identify cognitive States associated with perception of tools and dwellings.

SV Shinkareva — 2008-01-31T22:52:19-00:00

PLoS ONE, Vol. 3, No. 1. (2008)

Previous studies have succeeded in identifying the cognitive state corresponding to the perception of a set of depicted categories, such as tools, by analyzing the accompanying pattern of brain activity, measured with fMRI. The current research focused on identifying the cognitive state associated with a 4s viewing of an individual line drawing (1 of 10 familiar objects, 5 tools and 5 dwellings, such as a hammer or a castle). Here we demonstrate the ability to reliably (1) identify which of the 10 drawings a participant was viewing, based on that participant's characteristic whole-brain neural activation patterns, excluding visual areas; (2) identify the category of the object with even higher accuracy, based on that participant's activation; and (3) identify, for the first time, both individual objects and the category of the object the participant was viewing, based only on other participants' activation patterns. The voxels important for category identification were located similarly across participants, and distributed throughout the cortex, focused in ventral temporal perceptual areas but also including more frontal association areas (and somewhat left-lateralized). These findings indicate the presence of stable, distributed, communal, and identifiable neural states corresponding to object concepts.

Inverse retinotopy: Inferring the visual content of images from brain activation patterns

Bertrand Thirion — 2008-01-31T22:58:38-00:00

NeuroImage, Vol. 33, No. 4. (December 2006), pp. 1104-1116.

Traditional inference in neuroimaging consists in describing brain activations elicited and modulated by different kinds of stimuli. Recently, however, paradigms have been studied in which the converse operation is performed, thus inferring behavioral or mental states associated with activation images. Here, we use the well-known retinotopy of the visual cortex to infer the visual content of real or imaginary scenes from the brain activation patterns that they elicit. We present two decoding algorithms: an explicit technique, based on the current knowledge of the retinotopic structure of the visual areas, and an implicit technique, based on supervised classifiers. Both algorithms predicted the stimulus identity with significant accuracy. Furthermore, we extend this principle to mental imagery data: in five data sets, our algorithms could reconstruct and predict with significant accuracy a pattern imagined by the subjects.

Individual faces elicit distinct response patterns in human anterior temporal cortex

Nikolaus Kriegeskorte — 2007-12-18T19:48:02-00:00

Proceedings of the National Academy of Sciences, Vol. 104, No. 51. (18 December 2007), pp. 20600-20605.

Visual face identification requires distinguishing between thousands of faces we know. This computational feat involves a network of brain regions including the fusiform face area (FFA) and anterior inferotemporal cortex (aIT), whose roles in the process are not well understood. Here, we provide the first demonstration that it is possible to discriminate cortical response patterns elicited by individual face images with high-resolution functional magnetic resonance imaging (fMRI). Response patterns elicited by the face images were distinct in aIT but not in the FFA. Individual-level face information is likely to be present in both regions, but our data suggest that it is more pronounced in aIT. One interpretation is that the FFA detects faces and engages aIT for identification. 10.1073/pnas.0705654104

Neuronal Population Coding of Movement Direction

Apostolos Georgopoulos — 2008-01-31T23:03:35-00:00

Science, Vol. 233, No. 4771. (26 September 1986), pp. 1416-1419.

Although individual neurons in the arm area of the primate motor cortex are only broadly tuned to a particular direction in three-dimensional space, the animal can very precisely control the movement of its arm. The direction of movement was found to be uniquely predicted by the action of a population of motor cortical neurons. When individual cells were represented as vectors that make weighted contributions along the axis of their preferred direction (according to changes in their activity during the movement under consideration) the resulting vector sum of all cell vectors (population vector) was in a direction congruent with the direction of movement. This population vector can be monitored during various tasks, and similar measures in other neuronal populations could be of heuristic value where there is a neural representation of variables with vectorial attributes.

A temporal frequency-dependent functional architecture in human V1 revealed by high-resolution fMRI.

Pei Sun — 2007-10-17T10:01:37-00:00

Nat Neurosci (14 October 2007)

Although cortical neurons with similar functional properties often cluster together in a columnar organization, only ocular dominance columns, the columnar structure representing segregated anatomical input (from one of the two eyes), have been found in human primary visual cortex (V1). It has yet to be shown whether other columnar organizations that arise only from differential responses to stimulus properties also exist in human V1. Using high-resolution functional magnetic resonance imaging, we have found such a functional architecture containing domains that respond preferentially to either low or high temporal frequency.

Invariant visual representation by single neurons in the human brain

Quian Quiroga — 2005-06-23T02:21:22-00:00

Nature, Vol. 435, No. 7045., pp. 1102-1107.

Natural Vision Reveals Regional Specialization to Local Motion and to Contrast-Invariant, Global Flow in the Human Brain

A Bartels — 2008-02-01T01:18:06-00:00

Cereb. Cortex (5 July 2007), bhm107.

Visual changes in feature movies, like in real-live, can be partitioned into global flow due to self/camera motion, local/differential flow due to object motion, and residuals, for example, due to illumination changes. We correlated these measures with brain responses of human volunteers viewing movies in an fMRI scanner. Early visual areas responded only to residual changes, thus lacking responses to equally large motion-induced changes, consistent with predictive coding. Motion activated V5+ (MT+), V3A, medial posterior parietal cortex (mPPC) and, weakly, lateral occipital cortex (LOC). V5+ responded to local/differential motion and depended on visual contrast, whereas mPPC responded to global flow spanning the whole visual field and was contrast independent. mPPC thus codes for flow compatible with unbiased heading estimation in natural scenes and for the comparison of visual flow with nonretinal, multimodal motion cues in it or downstream. mPPC was functionally connected to anterior portions of V5+, whereas laterally neighboring putative homologue of lateral intraparietal area (LIP) connected with frontal eye fields. Our results demonstrate a progression of selectivity from local and contrast-dependent motion processing in V5+ toward global and contrast-independent motion processing in mPPC. The function, connectivity, and anatomical neighborhood of mPPC imply several parallels to monkey ventral intraparietal area (VIP). 10.1093/cercor/bhm107

Shaping of Motor Responses by Incentive Values through the Basal Ganglia

Benjamin Pasquereau — 2007-02-20T12:04:45-00:00

J. Neurosci., Vol. 27, No. 5. (31 January 2007), pp. 1176-1183.

The striatum is a key neural interface for cognitive and motor information processing in which associations between reward value and visual stimulus can be used to modify motor commands. It can guide action-selection processes that occur farther downstream in the basal ganglia (BG) circuit, by encoding the reward value of an action. Here, we report on the study of simultaneously recorded neurons in the dorsal striatum (input stage of the BG) and the internal pallidum (output stage of the BG) in two monkeys performing a center-out motor task in which the visual targets were associated with different reward probabilities. We show that the tuning curves of motor-related neurons in both structures are modulated by the value of the action before movement initiation and during its execution. The representations of values associated with different actions change dynamically during the task in the internal globus pallidus, with a significant increase in the number of encoding neurons for the chosen target at the onset of movement. This report sheds additional light on the functional differences between the input and output structures of the BG and supports the assertion that the dorsal basal ganglia are involved in movement-related decision-making processes based on incentive values. 10.1523/JNEUROSCI.3745-06.2007

Functionally specific reorganization in human premotor cortex.

J O'shea — 2007-05-14T15:47:40-00:00

Neuron, Vol. 54, No. 3. (3 May 2007), pp. 479-490.

After unilateral stroke, the dorsal premotor cortex (PMd) in the intact hemisphere is often more active during movement of an affected limb. Whether this contributes to motor recovery is unclear. Functional magnetic resonance imaging (fMRI) was used to investigate short-term reorganization in right PMd after transcranial magnetic stimulation (TMS) disrupted the dominant left PMd, which is specialized for action selection. Even when 1 Hz left PMd TMS had no effect on behavior, there was a compensatory increase in activity in right PMd and connected medial premotor areas. This activity was specific to task periods of action selection as opposed to action execution. Compensatory activation changes were both functionally specific and anatomically specific: the same pattern was not seen after TMS of left sensorimotor cortex. Subsequent TMS of the reorganized right PMd did disrupt performance. Thus, this pattern of functional reorganization has a causal role in preserving behavior after neuronal challenge.

How a lateralized brain supports symmetrical bimanual tasks.

RS Johansson — 2008-01-15T19:30:48-00:00

PLoS Biol, Vol. 4, No. 6. (June 2006)

A large repertoire of natural object manipulation tasks require precisely coupled symmetrical opposing forces by both hands on a single object. We asked how the lateralized brain handles this basic problem of spatial and temporal coordination. We show that the brain consistently appoints one of the hands as prime actor while the other assists, but the choice of acting hand is flexible. When study participants control a cursor by manipulating a tool held freely between the hands, the left hand becomes prime actor if the cursor moves directionally with the left-hand forces, whereas the right hand primarily acts if it moves with the opposing right-hand forces. In neurophysiological (electromyography, transcranial magnetic brain stimulation) and functional magnetic resonance brain imaging experiments we demonstrate that changes in hand assignment parallels a midline shift of lateralized activity in distal hand muscles, corticospinal pathways, and primary sensorimotor and cerebellar cortical areas. We conclude that the two hands can readily exchange roles as dominant actor in bimanual tasks. Spatial relationships between hand forces and goal motions determine hand assignments rather than habitual handedness. Finally, flexible role assignment of the hands is manifest at multiple levels of the motor system, from cortical regions all the way down to particular muscles.

Differential development of high-level visual cortex correlates with category-specific recognition memory.

Golijeh Golarai — 2007-03-19T17:28:28-00:00

Nat Neurosci (11 March 2007)

High-level visual cortex in humans includes functionally defined regions that preferentially respond to objects, faces and places. It is unknown how these regions develop and whether their development relates to recognition memory. We used functional magnetic resonance imaging to examine the development of several functionally defined regions including object (lateral occipital complex, LOC)-, face ('fusiform face area', FFA; superior temporal sulcus, STS)- and place ('parahippocampal place area', PPA)-selective cortices in children (ages 7-11), adolescents (12-16) and adults. Right FFA and left PPA volumes were substantially larger in adults than in children. This development occurred by expansion of FFA and PPA into surrounding cortex and was correlated with improved recognition memory for faces and places, respectively. In contrast, LOC and STS volumes and object-recognition memory remained constant across ages. Thus, the ventral stream undergoes a prolonged maturation that varies temporally across functional regions, is determined by brain region rather than stimulus category, and is correlated with the development of category-specific recognition memory.

Boosting slow oscillations during sleep potentiates memory

Lisa Marshall — 2006-11-06T04:08:12-00:00

Nature

Hippocampal remapping and grid realignment in entorhinal cortex

Marianne Fyhn — 2007-02-27T01:54:47-00:00

Nature (25 February 2007)

Lateral habenula as a source of negative reward signals in dopamine neurons

Masayuki Matsumoto — 2007-05-24T01:27:28-00:00

Nature (23 May 2007)

Dopamine-dependent prediction errors underpin reward-seeking behaviour in humans

Mathias Pessiglione — 2006-08-24T16:08:46-00:00

Nature, Vol. 442, No. 7106. (23 August 2006), pp. 1042-1045.

Dopamine neurons encode the better option in rats deciding between differently delayed or sized rewards

Matthew Roesch — 2007-11-27T17:36:53-00:00

Nature Neuroscience, Vol. 10, No. 12. (18 November 2007), pp. 1615-1624.

Different Processing Phases for Features, Figures, and Selective Attention in the Primary Visual Cortex.

Pieter R Roelfsema — 2007-12-10T15:29:41-00:00

Neuron, Vol. 56, No. 5. (6 December 2007), pp. 785-792.

Our visual system imposes structure onto images that usually contain a diversity of surfaces, contours, and colors. Psychological theories propose that there are multiple steps in this process that occur in hierarchically organized regions of the cortex: early visual areas register basic features, higher areas bind them into objects, and yet higher areas select the objects that are relevant for behavior. Here we test these theories by recording from the primary visual cortex (area V1) of monkeys. We demonstrate that the V1 neurons first register the features (at a latency of 48 ms), then segregate figures from the background (after 57 ms), and finally select relevant figures over irrelevant ones (after 137 ms). We conclude that the psychological processing stages map onto distinct time episodes that unfold in the visual cortex after the presentation of a new stimulus, so that area V1 may contribute to all these processing steps.

Feature-Based Attentional Modulations in the Absence of Direct Visual Stimulation.

John T Serences — 2007-07-23T13:50:50-00:00

Neuron, Vol. 55, No. 2. (19 July 2007), pp. 301-312.

When faced with a crowded visual scene, observers must selectively attend to behaviorally relevant objects to avoid sensory overload. Often this selection process is guided by prior knowledge of a target-defining feature (e.g., the color red when looking for an apple), which enhances the firing rate of visual neurons that are selective for the attended feature. Here, we used functional magnetic resonance imaging and a pattern classification algorithm to predict the attentional state of human observers as they monitored a visual feature (one of two directions of motion). We find that feature-specific attention effects spread across the visual field-even to regions of the scene that do not contain a stimulus. This spread of feature-based attention to empty regions of space may facilitate the perception of behaviorally relevant stimuli by increasing sensitivity to attended features at all locations in the visual field.

The Neural Site of Attention Matches the Spatial Scale of Perception

Jens-Max Hopf — 2008-02-01T05:49:24-00:00

J. Neurosci., Vol. 26, No. 13. (29 March 2006), pp. 3532-3540.

What is the neural locus of visual attention? Here we show that the locus is not fixed but instead changes rapidly to match the spatial scale of task-relevant information in the current scene. To accomplish this, we obtained electrical, magnetic, and hemodynamic measures of attention from human subjects while they detected large-scale or small-scale targets within multiscale stimulus patterns. Subjects did not know the scale of the target before stimulus onset, and yet the neural locus of attention-related activity between 250 and 300 ms varied according to the scale of the target. Specifically, maximal attention-related activity spread from a high-level, relatively anterior visual area (the lateral occipital complex) for large-scale targets to include a lower-level, more posterior area (visual area V4) for small-scale targets. This rapid change indicates that the neural locus of attention in visual cortex is not static but is instead determined rapidly and dynamically by means of an interaction between top-down task information and local information about the current visual input. 10.1523/JNEUROSCI.4510-05.2006

Direct Intracranial, fMRI, and Lesion Evidence for the Causal Role of Left Inferotemporal Cortex in Reading

Raphael Gaillard — 2008-02-01T05:52:21-00:00

Neuron, Vol. 50, No. 2. (20 April 2006), pp. 191-204.

Summary Models of the "visual word form system" postulate that a left occipitotemporal region implements the automatic visual word recognition required for efficient reading. This theory was assessed in a patient in whom reading was explored with behavioral measures, fMRI, and intracranial local field potentials. Prior to surgery, when reading was normal, fMRI revealed a normal mosaic of ventral visual selectivity for words, faces, houses, and tools. Intracranial recordings demonstrated that the left occipitotemporal cortex responded with a short latency to conscious but also to subliminal words. Surgery removed a small portion of word-responsive occipitotemporal cortex overlapping with the word-specific fMRI activation. The patient developed a marked reading deficit, while recognition of other visual categories remained intact. Furthermore, in the post-surgery fMRI map of visual cortex, only word-specific activations disappeared. Altogether, these results provide direct evidence for the causal role of the left occipitotemporal cortex in the recognition of visual words.

Phase patterns of neuronal responses reliably discriminate speech in human auditory cortex.

H Luo — 2007-06-27T18:29:13-00:00

Neuron, Vol. 54, No. 6. (21 June 2007), pp. 1001-1010.

How natural speech is represented in the auditory cortex constitutes a major challenge for cognitive neuroscience. Although many single-unit and neuroimaging studies have yielded valuable insights about the processing of speech and matched complex sounds, the mechanisms underlying the analysis of speech dynamics in human auditory cortex remain largely unknown. Here, we show that the phase pattern of theta band (4-8 Hz) responses recorded from human auditory cortex with magnetoencephalography (MEG) reliably tracks and discriminates spoken sentences and that this discrimination ability is correlated with speech intelligibility. The findings suggest that an approximately 200 ms temporal window (period of theta oscillation) segments the incoming speech signal, resetting and sliding to track speech dynamics. This hypothesized mechanism for cortical speech analysis is based on the stimulus-induced modulation of inherent cortical rhythms and provides further evidence implicating the syllable as a computational primitive for the representation of spoken language.

Dynamics of language reorganization after stroke.

D Saur — 2006-08-06T17:59:58-00:00

Brain, Vol. 129, No. Pt 6. (June 2006), pp. 1371-1384.

Previous functional imaging studies of chronic stroke patients with aphasia suggest that recovery of language occurs in a pre-existing, bilateral network with an upregulation of undamaged areas and a recruitment of perilesional tissue and homologue right language areas. The present study aimed at identifying the dynamics of reorganization in the language system by repeated functional MRI (fMRI) examinations with parallel language testing from the acute to the chronic stage. We examined 14 patients with aphasia due to an infarction of the left middle cerebral artery territory and an age-matched control group with an auditory comprehension task in an event-related design. Control subjects were scanned once, whereas patients were scanned repeatedly at three consecutive dates. All patients recovered clinically as shown by a set of aphasia tests. In the acute phase [mean: 1.8 days post-stroke (dps)], patients' group analysis showed little early activation of non-infarcted left-hemispheric language structures, while in the subacute phase (mean: 12.1 dps) a large increase of activation in the bilateral language network with peak activation in the right Broca-homologue (BHo) was observed. A direct comparison of both examinations revealed the strongest increase of activation in the right BHo and supplementary motor area (SMA). These upregulated areas also showed the strongest correlation between improved language function and increased activation (r(BHo) = 0.88, r(SMA) = 0.92). In the chronic phase (mean: 321 dps), a normalization of activation with a re-shift of peak activation to left-hemispheric language areas was observed, associated with further language improvement. The data suggest that brain reorganization during language recovery proceeds in three phases: a strongly reduced activation of remaining left language areas in the acute phase is followed by an upregulation with recruitment of homologue language zones, which correlates with language improvement. Thereafter, a normalization of activation is observed, possibly reflecting consolidation in the language system.

The representation of economic value in the orbitofrontal cortex is invariant for changes of menu

Camillo Padoa-Schioppa — 2007-12-27T17:57:48-00:00

Nature Neuroscience, Vol. 11, No. 1. (09 December 2007), pp. 95-102.

Time Discounting for Primary Rewards

Samuel Mcclure — 2007-05-23T18:23:55-00:00

J. Neurosci., Vol. 27, No. 21. (23 May 2007), pp. 5796-5804.

Previous research, involving monetary rewards, found that limbic reward-related areas show greater activity when an intertemporal choice includes an immediate reward than when the options include only delayed rewards. In contrast, the lateral prefrontal and parietal cortex (areas commonly associated with deliberative cognitive processes, including future planning) respond to intertemporal choices in general but do not exhibit sensitivity to immediacy (McClure et al., 2004). The current experiments extend these findings to primary rewards (fruit juice or water) and time delays of minutes instead of weeks. Thirsty subjects choose between small volumes of drinks delivered at precise times during the experiment (e.g., 2 ml now vs 3 ml in 5 min). Consistent with previous findings, limbic activation was greater for choices between an immediate reward and a delayed reward than for choices between two delayed rewards, whereas the lateral prefrontal cortex and posterior parietal cortex responded similarly whether choices were between an immediate and a delayed reward or between two delayed rewards. Moreover, relative activation of the two sets of brain regions predicts actual choice behavior. A second experiment finds that when the delivery of all rewards is offset by 10 min (so that the earliest available juice reward in any choice is 10 min), no differential activity is observed in limbic reward-related areas for choices involving the earliest versus only more delayed rewards. We discuss implications of this finding for differences between primary and secondary rewards. 10.1523/JNEUROSCI.4246-06.2007

Reward Timing in the Primary Visual Cortex

Marshall Shuler — 2006-03-17T19:30:52-00:00

Science, Vol. 311, No. 5767. (17 March 2006), pp. 1606-1609.

We discovered that when adult rats experience an association between visual stimuli and subsequent rewards, the responses of a substantial fraction of neurons in the primary visual cortex evolve from those that relate solely to the physical attributes of the stimuli to those that accurately predict the timing of reward. In addition to revealing a remarkable type of response plasticity in adult V1, these data demonstrate that reward-timing activity--a "higher" brain function--can occur very early in sensory-processing paths. These findings challenge the traditional interpretation of activity in the primary visual cortex.

Inverted-U dopamine D1 receptor actions on prefrontal neurons engaged in working memory

Susheel Vijayraghavan — 2007-02-23T22:13:48-00:00

Nature Neuroscience, Vol. 10, No. 3. (04 February 2007), pp. 376-384.

Categorization of behavioural sequences in the prefrontal cortex

Keisetsu Shima — 2006-12-20T20:06:12-00:00

Nature (20 December 2006)

Neural measures reveal individual differences in controlling access to working memory

Edward Vogel — 2005-11-23T18:52:37-00:00

Nature, Vol. 438, No. 7067., pp. 500-503.

Unconscious activation of the cognitive control system in the human prefrontal cortex.

HC Lau — 2007-10-25T22:03:31-00:00

J Neurosci, Vol. 27, No. 21. (23 May 2007), pp. 5805-5811.

Using functional magnetic resonance imaging, we tested whether unconscious information can influence the cognitive control system in the human prefrontal cortex. Volunteers had to prepare to perform either a phonological judgment or a semantic judgment on an upcoming word, based on the instruction given at the beginning of each trial. However, in some trials they were visually primed to prepare for the alternative (i.e., "wrong") task, and this impaired their performance. This priming effect is taken to depend on unconscious processes because the effect was present even when the volunteers could only discriminate the identity of the primes at chance level. Furthermore, the effect was stronger when the visibility of the prime was near zero than when the visibility of the prime was significantly higher. When volunteers were unconsciously primed to perform the alternative task, there was also decreased neural activity in the brain areas relevant to the instructed task and increased neural activity in the brain areas relevant to the alternative task, which shows that the volunteers were actually engaged in the wrong task, instead of simply being distracted. Activity in the mid-dorsolateral prefrontal cortex was also found to be associated with this unconscious priming effect. These results suggest that the cognitive control system in the prefrontal cortex is not exclusively driven by conscious information, as has been believed previously.

Top-Down Versus Bottom-Up Control of Attention in the Prefrontal and Posterior Parietal Cortices

Timothy Buschman — 2007-03-30T13:28:45-00:00

Science, Vol. 315, No. 5820. (30 March 2007), pp. 1860-1862.

Attention can be focused volitionally by "top-down" signals derived from task demands and automatically by "bottom-up" signals from salient stimuli. The frontal and parietal cortices are involved, but their neural activity has not been directly compared. Therefore, we recorded from them simultaneously in monkeys. Prefrontal neurons reflected the target location first during top-down attention, whereas parietal neurons signaled it earlier during bottom-up attention. Synchrony between frontal and parietal areas was stronger in lower frequencies during top-down attention and in higher frequencies during bottom-up attention. This result indicates that top-down and bottom-up signals arise from the frontal and sensory cortex, respectively, and different modes of attention may emphasize synchrony at different frequencies. 10.1126/science.1138071

Switching from automatic to controlled action by monkey medial frontal cortex

Masaki Isoda — 2007-01-27T11:53:28-00:00

Nature Neuroscience, Vol. 10, No. 2. (21 January 2007), pp. 240-248.

Neural mechanisms of genetic risk for impulsivity and violence in humans.

Andreas Meyer-Lindenberg — 2006-03-31T18:15:44-00:00

Proc Natl Acad Sci U S A (28 March 2006)

Neurobiological factors contributing to violence in humans remain poorly understood. One approach to this question is examining allelic variation in the X-linked monoamine oxidase A (MAOA) gene, previously associated with impulsive aggression in animals and humans. Here, we have studied the impact of a common functional polymorphism in MAOA on brain structure and function assessed with MRI in a large sample of healthy human volunteers. We show that the low expression variant, associated with increased risk of violent behavior, predicted pronounced limbic volume reductions and hyperresponsive amygdala during emotional arousal, with diminished reactivity of regulatory prefrontal regions, compared with the high expression allele. In men, the low expression allele is also associated with changes in orbitofrontal volume, amygdala and hippocampus hyperreactivity during aversive recall, and impaired cingulate activation during cognitive inhibition. Our data identify differences in limbic circuitry for emotion regulation and cognitive control that may be involved in the association of MAOA with impulsive aggression, suggest neural systems-level effects of X-inactivation in human brain, and point toward potential targets for a biological approach toward violence.

The Neural Signature of Social Norm Compliance

Manfred Spitzer — 2008-02-01T06:26:08-00:00

Neuron, Vol. 56, No. 1. (4 October 2007), pp. 185-196.

Summary All known human societies establish social order by punishing violators of social norms. However, little is known about how the brain processes the punishment threat associated with norm violations. We use fMRI to study the neural circuitry behind social norm compliance by comparing a treatment in which norm violations can be punished with a control treatment in which punishment is impossible. Individuals' increase in norm compliance when punishment is possible exhibits a strong positive correlation with activations in the lateral orbitofrontal cortex and right dorsolateral prefrontal cortex. Moreover, lateral orbitofrontal cortex activity is strongly correlated with Machiavellian personality characteristics. These findings indicate a neural network involved in social norm compliance that might constitute an important basis for human sociality. Different activations of this network reveal individual differences in the behavioral response to the punishment threat and might thus provide a deeper understanding of the neurobiological sources of pathologies such as antisocial personality disorder.

Damage to the prefrontal cortex increases utilitarian moral judgements.

Michael Koenigs — 2007-03-23T19:19:31-00:00

Nature (21 March 2007)

The psychological and neurobiological processes underlying moral judgement have been the focus of many recent empirical studies. Of central interest is whether emotions play a causal role in moral judgement, and, in parallel, how emotion-related areas of the brain contribute to moral judgement. Here we show that six patients with focal bilateral damage to the ventromedial prefrontal cortex (VMPC), a brain region necessary for the normal generation of emotions and, in particular, social emotions, produce an abnormally 'utilitarian' pattern of judgements on moral dilemmas that pit compelling considerations of aggregate welfare against highly emotionally aversive behaviours (for example, having to sacrifice one person's life to save a number of other lives). In contrast, the VMPC patients' judgements were normal in other classes of moral dilemmas. These findings indicate that, for a selective set of moral dilemmas, the VMPC is critical for normal judgements of right and wrong. The findings support a necessary role for emotion in the generation of those judgements.