2012年9月27日木曜日

Disruption of Reconsolidation Erases a Fear Memory Trace in the Human Amygdala


Thomas Agren, Jonas Engman, Andreas Frick, Johannes Björkstrand, Elna-Marie Larsson, Tomas Furmark, Mats Fredrikson
Science 21 September 2012: Vol. 337 no. 6101 pp. 1550-1552

Memories become labile when recalled. In humans and rodents alike, reactivated fear memories can be attenuated by disrupting reconsolidation with extinction training. Using functional brain imaging, we found that, after a conditioned fear memory was formed, reactivation and reconsolidation left a memory trace in the basolateral amygdala that predicted subsequent fear expression and was tightly coupled to activity in the fear circuit of the brain. In contrast, reactivation followed by disrupted reconsolidation suppressed fear, abolished the memory trace, and attenuated fear-circuit connectivity. Thus, as previously demonstrated in rodents, fear memory suppression resulting from behavioral disruption of reconsolidation is amygdala-dependent also in humans, which supports an evolutionarily conserved memory-update mechanism.

2012年9月26日水曜日

Cognitive Regulation during Decision Making Shifts Behavioral Control between Ventromedial and Dorsolateral Prefrontal Value Systems


Cendri A. Hutcherson, Hilke Plassmann, James J. Gross, and Antonio Rangel
J. Neurosci. 2012;32 13543-13554
http://www.jneurosci.org/cgi/content/abstract/32/39/13543?etoc

Cognitive regulation is often used to influence behavioral outcomes. However, the computational and neurobiological mechanisms by which it affects behavior remain unknown. We studied this issue using an fMRI task in which human participants used cognitive regulation to upregulate and downregulate their cravings for foods at the time of choice. We found that activity in both ventromedial prefrontal cortex (vmPFC) and dorsolateral prefrontal cortex (dlPFC) correlated with value. We also found evidence that two distinct regulatory mechanisms were at work: value modulation, which operates by changing the values assigned to foods in vmPFC and dlPFC at the time of choice, and behavioral control modulation, which operates by changing the relative influence of the vmPFC and dlPFC value signals on the action selection process used to make choices. In particular, during downregulation, activation decreased in the value-sensitive region of dlPFC (indicating value modulation) but not in vmPFC, and the relative contribution of the two value signals to behavior shifted toward the dlPFC (indicating behavioral control modulation). The opposite pattern was observed during upregulation: activation increased in vmPFC but not dlPFC, and the relative contribution to behavior shifted toward the vmPFC. Finally, ventrolateral PFC and posterior parietal cortex were more active during both upregulation and downregulation, and were functionally connected with vmPFC and dlPFC during cognitive regulation, which suggests that they help to implement the changes to the decision-making circuitry generated by cognitive regulation.

2012年9月25日火曜日

Differential Representations of Prior and Likelihood Uncertainty in the Human Brain


Iris Vilares, James D. Howard, Hugo L. Fernandes, Jay A. Gottfried, Konrad P. Kording
Current Biology, Volume 22, Issue 18, 1641-1648, 26 July 2012

Background
Uncertainty shapes our perception of the world and the decisions we make. Two aspects of uncertainty are commonly distinguished: uncertainty in previously acquired knowledge (prior) and uncertainty in current sensory information (likelihood). Previous studies have established that humans can take both types of uncertainty into account, often in a way predicted by Bayesian statistics. However, the neural representations underlying these parameters remain poorly understood.

Results
By varying prior and likelihood uncertainty in a decision-making task while performing neuroimaging in humans, we found that prior and likelihood uncertainty had quite distinct representations. Whereas likelihood uncertainty activated brain regions along the early stages of the visuomotor pathway, representations of prior uncertainty were identified in specialized brain areas outside this pathway, including putamen, amygdala, insula, and orbitofrontal cortex. Furthermore, the magnitude of brain activity in the putamen predicted individuals' personal tendencies to rely more on either prior or current information.

Conclusions
Our results suggest different pathways by which prior and likelihood uncertainty map onto the human brain and provide a potential neural correlate for higher reliance on current or prior knowledge. Overall, these findings offer insights into the neural pathways that may allow humans to make decisions close to the optimal defined by a Bayesian statistical framework.

2012年9月19日水曜日

An Agent Independent Axis for Executed and Modeled Choice in Medial Prefrontal Cortex


Antoinette Nicolle, Miriam C. Klein-Flügge, Laurence T. Hunt, Ivo Vlaev, Raymond J. Dolan, Timothy E.J. Behrens
Neuron, Volume 75, Issue 6, 1114-1121, 20 September 2012

Adaptive success in social animals depends on an ability to infer the likely actions of others. Little is known about the neural computations that underlie this capacity. Here, we show that the brain models the values and choices of others even when these values are currently irrelevant. These modeled choices use the same computations that underlie our own choices, but are resolved in a distinct neighboring medial prefrontal brain region. Crucially, however, when subjects choose on behalf of a partner instead of themselves, these regions exchange their functional roles. Hence, regions that represented values of the subject’s executed choices now represent the values of choices executed on behalf of the partner, and those that previously modeled the partner now model the subject. These data tie together neural computations underlying self-referential and social inference, and in so doing establish a new functional axis characterizing the medial wall of prefrontal cortex.

Spontaneous giving and calculated greed


David G. Rand, Joshua D. Greene & Martin A. Nowak
Nature 489, 427–430 (20 September 2012)

公共財ゲーム。協力者の方が反応時間が短い。被験者に速く(遅く)意思決定させると協力率が上がる(下がる)。直観的に(よく考えて)決定させると協力率が上がる(下がる)。→協力は自動的・デフォルト的処理である(裏切りは計算や熟考を要する処理)。

Cooperation is central to human social behaviour1, 2, 3, 4, 5, 6, 7, 8, 9. However, choosing to cooperate requires individuals to incur a personal cost to benefit others. Here we explore the cognitive basis of cooperative decision-making in humans using a dual-process framework10, 11, 12, 13, 14, 15, 16, 17, 18. We ask whether people are predisposed towards selfishness, behaving cooperatively only through active self-control; or whether they are intuitively cooperative, with reflection and prospective reasoning favouring ‘rational’ self-interest. To investigate this issue, we perform ten studies using economic games. We find that across a range of experimental designs, subjects who reach their decisions more quickly are more cooperative. Furthermore, forcing subjects to decide quickly increases contributions, whereas instructing them to reflect and forcing them to decide slowly decreases contributions. Finally, an induction that primes subjects to trust their intuitions increases contributions compared with an induction that promotes greater reflection. To explain these results, we propose that cooperation is intuitive because cooperative heuristics are developed in daily life where cooperation is typically advantageous. We then validate predictions generated by this proposed mechanism. Our results provide convergent evidence that intuition supports cooperation in social dilemmas, and that reflection can undermine these cooperative impulses.

2012年9月18日火曜日

Monkeys benefit from reciprocity without the cognitive burden

サルの互恵的行動は「しっぺ返し」的動機に起因しない。

Malini Suchak and Frans B. M. de Waal
PNAS September 18, 2012 vol. 109 no. 38 15191-15196

The debate about the origins of human prosociality has focused on the presence or absence of similar tendencies in other species, and, recently, attention has turned to the underlying mechanisms. We investigated whether direct reciprocity could promote prosocial behavior in brown capuchin monkeys (Cebus apella). Twelve capuchins tested in pairs could choose between two tokens, with one being “prosocial” in that it rewarded both individuals (i.e., 1/1), and the other being “selfish” in that it rewarded the chooser only (i.e., 1/0). Each monkey’s choices with a familiar partner from their own group was compared with choices when paired with a partner from a different group. Capuchins were spontaneously prosocial, selecting the prosocial option at the same rate regardless of whether they were paired with an in-group or out-group partner. This indicates that interaction outside of the experimental setting played no role. When the paradigm was changed, such that both partners alternated making choices, prosocial preference significantly increased, leading to mutualistic payoffs. As no contingency could be detected between an individual’s choice and their partner’s previous choice, and choices occurred in rapid succession, reciprocity seemed of a relatively vague nature akin to mutualism. Having the partner receive a better reward than the chooser (i.e., 1/2) during the alternating condition increased the payoffs of mutual prosociality, and prosocial choice increased accordingly. The outcome of several controls made it hard to explain these results on the basis of reward distribution or learned preferences, and rather suggested that joint action promotes prosociality, resulting in so-called attitudinal reciprocity.

Lateralization of observational fear learning at the cortical but not thalamic level in mice


Sangwoo Kim, Ferenc Mátyás, Sukchan Lee, László Acsády, and Hee-Sup Shin
PNAS September 18, 2012 vol. 109 no. 38 15497-15501

Major cognitive and emotional faculties are dominantly lateralized in the human cerebral cortex. The mechanism of this lateralization has remained elusive owing to the inaccessibility of human brains to many experimental manipulations. In this study we demonstrate the hemispheric lateralization of observational fear learning in mice. Using unilateral inactivation as well as electrical stimulation of the anterior cingulate cortex (ACC), we show that observational fear learning is controlled by the right but not the left ACC. In contrast to the cortex, inactivation of either left or right thalamic nuclei, both of which are in reciprocal connection to ACC, induced similar impairment of this behavior. The data suggest that lateralization of negative emotions is an evolutionarily conserved trait and mainly involves cortical operations. Lateralization of the observational fear learning behavior in a rodent model will allow detailed analysis of cortical asymmetry in cognitive functions.

2012年9月15日土曜日

J1ビザ面接@アメリカ大使館


J1ビザ申請のためアメリカ大使館に行ってきました。

【事前の準備】

参考にしたのは、
http://d.hatena.ne.jp/oxon/20100127/1264571940
http://www.joten.info/misc/living_in_US.html
http://hontolab.org/dailylife/visa-applicaiton/
など。
もちろん、アメリカ大使館のページを隅々まで読み込み、諸々確認しましたよ。
http://www.ustraveldocs.com/jp_jp/jp-niv-typej.asp

用意した書類は、
・DS-2019
受入先の大学に発行してもらう。
なお、その際には「学振の採用証明(英文、給与額記載)」と「CV(履歴書)」が必要。
また、その後に色々と書類にやり取りしたりで、結局合計一ヶ月強かかった。

・DS160
DS-2019の情報を基にWebで作成するが、とにかく入力する情報が膨大。
一定時間経過するとタイムアウトするので、申請番号を書き留めておく。そして、こまめにセーブ。
また、写真データ、過去の渡米歴なども必要。
ここでトラブル発生。UPした写真が最後の確認ページで表示されず、「PHOTO ARCHIVED」という文字だけが(直前のページで、「写真のUPは成功しました」とは出てたけど…)。
どうしようもないので、確認ページを「PHOTO ARCHIVED」のままで印刷する(←結局、面接では大丈夫でした!)。

・I-901 SEVIS費用支払い証明
DS-2019に記載されている情報が必要。
最終ページを印刷する。

・面接予約確認書
Webで予約した際に取得。印刷する。

・成績証明
大学院博士後期課程には授業がなかったため、修了証明書で代替。

・受入先の大学からのInvitation Letter
・ビザ申請費用振込証明(ATMのPayEasy使用:明細をDS160の確認ページに貼付)
・証明写真(5cm x 5cm:DS160の確認ページに貼付)
・婚姻証明(原本+英訳コピー)
・財政証明(学振の採用証明書:英文/給与額記載)
・過去10年分のパスポート

これらの書類をクリアファイルに入れて持って行く。
なお、書類を入れる順番が決まっているので注意。
http://japan2.usembassy.gov/pdfs/wwwf-visa-j-docs-arrangement.pdf
注:最近はレターパックは不要。郵送代はビザ申請料金に含まれている。

【面接当日】

・7:45頃
溜池山王のアメリカ大使館に到着し、門の前に並ぶ(面接予約は8:15)。
朝の微妙な時間でトイレに行きたくて苦しむ(危うくう◯こを漏らしそうに:笑)。

・8:00
入念なセキュリティーチェックを受けて入館開始。
携帯電話などはここで預ける。

・8:10頃
建物の入り口でもう一度セキュリティーチェック。
その後、持参した書類について簡単なチェックを受け、整理番号をもらう(J2ビザを申請する妻と二人で一つの整理番号でした)。
ここでやっとトイレに。助かった…

・8:30頃
書類不備で呼び出される。
「DS160の写真UPの件か!?」とビビったけど、実際は「婚姻証明の日本語原本を付けて下さい」と言われる。
持参してたのでそれを係の人に渡す(念のため持って来てて良かった…)。
そして再び待機。

・9:30頃
呼び出されて指紋採取。
指が乾いていたのか、何度かやり直したが2、3分で終了。
再び待機。

10:00頃
いよいよ(やっと)面接の呼び出し。
妻と一緒にブース(銀行の窓口みたいな感じ、立ったまま面接を受ける)に並ぶ。
(なお、この呼び出し。すぐ終わる人は2、3組まとめて呼び出されているっぽい。我々もまとめて呼び出された)
面接での質問は、ぼくに対しては、
-どこに行くのですか?
-何を研究するのですか?
-給料はどこから出るのですか?
-博士号はどこの大学で取得しましたか?
妻に対しては、
-短期間でパスポートを更新しているのはなぜですか?
(結婚後、姓を変更するためにパスポートを更新していた)
など簡単なものばかりでした。
領事はイケメンでとってもナイスな人で、面接は5分程度で終了!

・3日後
無事にビザが到着。
やったー。
めでたしめでたしでした…

2012年9月12日水曜日

Distinct Information Representation and Processing for Goal-Directed Behavior in the Dorsolateral and Ventrolateral Prefrontal Cortex and the Dorsal Premotor Cortex


Tomoko Yamagata, Yoshihisa Nakayama, Jun Tanji, and Eiji Hoshi
J. Neurosci. 2012;32 12934-12949
http://www.jneurosci.org/cgi/content/abstract/32/37/12934?etoc

Although the lateral prefrontal cortex (lPFC) and dorsal premotor cortex (PMd) are thought to be involved in goal-directed behavior, the specific roles of each area still remain elusive. To characterize and compare neuronal activity in two sectors of the lPFC [dorsal (dlPFC) and ventral (vlPFC)] and the PMd, we designed a behavioral task for monkeys to explore the differences in their participation in four aspects of information processing: encoding of visual signals, behavioral goal retrieval, action specification, and maintenance of relevant information. We initially presented a visual object (an instruction cue) to instruct a behavioral goal (reaching to the right or left of potential targets). After a subsequent delay, a choice cue appeared at various locations on a screen, and the animals could specify an action to achieve the behavioral goal. We found that vlPFC neurons amply encoded object features of the instruction cues for behavioral goal retrieval and, subsequently, spatial locations of the choice cues for specifying the actions. By contrast, dlPFC and PMd neurons rarely encoded the object features, although they reflected the behavioral goals throughout the delay period. After the appearance of the choice cues, the PMd held information for action throughout the specification and preparation of reaching movements. Remarkably, lPFC neurons represented information for the behavioral goal continuously, even after the action specification as well as during its execution. These results indicate that area-specific representation and information processing at progressive stages of the perception–action transformation in these areas underlie goal-directed behavior.

Dynamic Estimation of Task-Relevant Variance in Movement under Risk


Michael S. Landy, Julia Trommershauser, and Nathaniel D. Daw
J. Neurosci. 2012;32 12702-12711
http://www.jneurosci.org/cgi/content/abstract/32/37/12702?etoc

Humans take into account their own movement variability as well as potential consequences of different movement outcomes in planning movement trajectories. When variability increases, planned movements are altered so as to optimize expected consequences of the movement. Past research has focused on the steady-state responses to changing conditions of movement under risk. Here, we study the dynamics of such strategy adjustment in a visuomotor decision task in which subjects reach toward a display with regions that lead to rewards and penalties, under conditions of changing uncertainty. In typical reinforcement learning tasks, subjects should base subsequent strategy by computing an estimate of the mean outcome (e.g., reward) in recent trials. In contrast, in our task, strategy should be based on a dynamic estimate of recent outcome uncertainty (i.e., squared error). We find that subjects respond to increased movement uncertainty by aiming movements more conservatively with respect to penalty regions, and that the estimate of uncertainty they use is well characterized by a weighted average of recent squared errors, with higher weights given to more recent trials.

Neural Dynamics of Choice: Single-Trial Analysis of Decision-Related Activity in Parietal Cortex


Anil Bollimunta, Douglas Totten, and Jochen Ditterich
J. Neurosci. 2012;32 12684-12701
http://www.jneurosci.org/cgi/content/abstract/32/37/12684?etoc

Previous neurophysiological studies of perceptual decision-making have focused on single-unit activity, providing insufficient information about how individual decisions are accomplished. For the first time, we recorded simultaneously from multiple decision-related neurons in parietal cortex of monkeys performing a perceptual decision task and used these recordings to analyze the neural dynamics during single trials. We demonstrate that decision-related lateral intraparietal area neurons typically undergo gradual changes in firing rate during individual decisions, as predicted by mechanisms based on continuous integration of sensory evidence. Furthermore, we identify individual decisions that can be described as a change of mind: the decision circuitry was transiently in a state associated with a different choice before transitioning into a state associated with the final choice. These changes of mind reflected in monkey neural activity share similarities with previously reported changes of mind reflected in human behavior.

2012年9月11日火曜日

No third-party punishment in chimpanzees


Katrin Riedl, Keith Jensen, Josep Call, and Michael Tomasello
PNAS September 11, 2012 vol. 109 no. 37 14824-14829

Punishment can help maintain cooperation by deterring free-riding and cheating. Of particular importance in large-scale human societies is third-party punishment in which individuals punish a transgressor or norm violator even when they themselves are not affected. Nonhuman primates and other animals aggress against conspecifics with some regularity, but it is unclear whether this is ever aimed at punishing others for noncooperation, and whether third-party punishment occurs at all. Here we report an experimental study in which one of humans' closest living relatives, chimpanzees (Pan troglodytes), could punish an individual who stole food. Dominants retaliated when their own food was stolen, but they did not punish when the food of third-parties was stolen, even when the victim was related to them. Third-party punishment as a means of enforcing cooperation, as humans do, might therefore be a derived trait in the human lineage.

Emergence of social complexity among coastal hunter-gatherers in the Atacama Desert of northern Chile


Pablo A. Marquet, Calogero M. Santoro, Claudio Latorre, Vivien G. Standen, Sebastián R. Abades, Marcelo M. Rivadeneira, Bernardo Arriaza, and Michael E. Hochberg
PNAS September 11, 2012 vol. 109 no. 37 14754-14760

The emergence of complex cultural practices in simple hunter-gatherer groups poses interesting questions on what drives social complexity and what causes the emergence and disappearance of cultural innovations. Here we analyze the conditions that underlie the emergence of artificial mummification in the Chinchorro culture in the coastal Atacama Desert in northern Chile and southern Peru. We provide empirical and theoretical evidence that artificial mummification appeared during a period of increased coastal freshwater availability and marine productivity, which caused an increase in human population size and accelerated the emergence of cultural innovations, as predicted by recent models of cultural and technological evolution. Under a scenario of increasing population size and extreme aridity (with little or no decomposition of corpses) a simple demographic model shows that dead individuals may have become a significant part of the landscape, creating the conditions for the manipulation of the dead that led to the emergence of complex mortuary practices.

Evolution of cooperation and skew under imperfect information


Erol Akçay, Adam Meirowitz, Kristopher W. Ramsay, and Simon A. Levin
PNAS September 11, 2012 vol. 109 no. 37 14936-14941

The evolution of cooperation in nature and human societies depends crucially on how the benefits from cooperation are divided and whether individuals have complete information about their payoffs. We tackle these questions by adopting a methodology from economics called mechanism design. Focusing on reproductive skew as a case study, we show that full cooperation may not be achievable due to private information over individuals’ outside options, regardless of the details of the specific biological or social interaction. Further, we consider how the structure of the interaction can evolve to promote the maximum amount of cooperation in the face of the informational constraints. Our results point to a distinct avenue for investigating how cooperation can evolve when the division of benefits is flexible and individuals have private information.

2012年9月5日水曜日

Temporal Integration of Olfactory Perceptual Evidence in Human Orbitofrontal Cortex


Nicholas E. Bowman, Konrad P. Kording, Jay A. Gottfried
Neuron, Volume 75, Issue 5, 916-927, 6 September 2012

Given a noisy sensory world, the nervous system integrates perceptual evidence over time to optimize decision-making. Neurophysiological accumulation of sensory information is well-documented in the animal visual system, but how such mechanisms are instantiated in the human brain remains poorly understood. Here we combined psychophysical techniques, drift-diffusion modeling, and functional magnetic resonance imaging (fMRI) to establish that odor evidence integration in the human olfactory system enhances discrimination on a two-alternative forced-choice task. Model-based measures of fMRI brain activity highlighted a ramp-like increase in orbitofrontal cortex (OFC) that peaked at the time of decision, conforming to predictions derived from an integrator model. Combined behavioral and fMRI data further suggest that decision bounds are not fixed but collapse over time, facilitating choice behavior in the presence of low-quality evidence. These data highlight a key role for the orbitofrontal cortex in resolving sensory uncertainty and provide substantiation for accumulator models of human perceptual decision-making.

Reward Cues in Space: Commonalities and Differences in Neural Coding by Hippocampal and Ventral Striatal Ensembles


Carien S. Lansink, Jadin C. Jackson, Jan V. Lankelma, Rutsuko Ito, Trevor W. Robbins, Barry J. Everitt, and Cyriel M.A. Pennartz
J. Neurosci. 2012;32 12444-12459

Forming place-reward associations critically depends on the integrity of the hippocampal–ventral striatal system. The ventral striatum (VS) receives a strong hippocampal input conveying spatial-contextual information, but it is unclear how this structure integrates this information to invigorate reward-directed behavior. Neuronal ensembles in rat hippocampus (HC) and VS were simultaneously recorded during a conditioning task in which navigation depended on path integration. In contrast to HC, ventral striatal neurons showed low spatial selectivity, but rather coded behavioral task phases toward reaching goal sites. Outcome-predicting cues induced a remapping of firing patterns in the HC, consistent with its role in episodic memory. VS remapped in conjunction with the HC, indicating that remapping can take place in multiple brain regions engaged in the same task. Subsets of ventral striatal neurons showed a “flip” from high activity when cue lights were illuminated to low activity in intertrial intervals, or vice versa. The cues induced an increase in spatial information transmission and sparsity in both structures. These effects were paralleled by an enhanced temporal specificity of ensemble coding and a more accurate reconstruction of the animal's position from population firing patterns. Altogether, the results reveal strong differences in spatial processing between hippocampal area CA1 and VS, but indicate similarities in how discrete cues impact on this processing.

Separate, Causal Roles of the Caudate in Saccadic Choice and Execution in a Perceptual Decision Task


Long Ding, Joshua I. Gold
Neuron, Volume 75, Issue 5, 865-874, 6 September 2012

In contrast to the well-established roles of the striatum in movement generation and value-based decisions, its contributions to perceptual decisions lack direct experimental support. Here, we show that electrical microstimulation in the monkey caudate nucleus influences both choice and saccade response time on a visual motion discrimination task. Within a drift-diffusion framework, these effects consist of two components. The perceptual component biases choices toward ipsilateral targets, away from the neurons’ predominantly contralateral response fields. The choice bias is consistent with a nonzero starting value of the diffusion process, which increases and decreases decision times for contralateral and ipsilateral choices, respectively. The nonperceptual component decreases and increases nondecision times toward contralateral and ipsilateral targets, respectively, consistent with the caudate’s role in saccade generation. The results imply a causal role for the caudate in perceptual decisions used to select saccades that may be distinct from its role in executing those saccades.

Predicting Perceptual Decision Biases from Early Brain Activity


Stefan Bode, David K. Sewell, Simon Lilburn, Jason D. Forte, Philip L. Smith, and Jutta Stahl
J. Neurosci. 2012;32 12488-12498
http://www.jneurosci.org/cgi/content/abstract/32/36/12488?etoc

Perceptual decision making is believed to be driven by the accumulation of sensory evidence following stimulus encoding. More controversially, some studies report that neural activity preceding the stimulus also affects the decision process. We used a multivariate pattern classification approach for the analysis of the human electroencephalogram (EEG) to decode choice outcomes in a perceptual decision task from spatially and temporally distributed patterns of brain signals. When stimuli provided discriminative information, choice outcomes were predicted by neural activity following stimulus encoding; when stimuli provided no discriminative information, choice outcomes were predicted by neural activity preceding the stimulus. Moreover, in the absence of discriminative information, the recent choice history primed the choices on subsequent trials. A diffusion model fitted to the choice probabilities and response time distributions showed that the starting point of the evidence accumulation process was shifted toward the previous choice, consistent with the hypothesis that choice priming biases the accumulation process toward a decision boundary. This bias is reflected in prestimulus brain activity, which, in turn, becomes predictive of future decisions. Our results provide a model of how non-stimulus-driven decision making in humans could be accomplished on a neural level.

2012年9月4日火曜日

Lesion mapping of cognitive control and value-based decision making in the prefrontal cortex


Jan Gläscher, Ralph Adolphs, Hanna Damasio, Antoine Bechara, David Rudrauf, Matthew Calamia, Lynn K. Paul, and Daniel Tranel
PNAS September 4, 2012 vol. 109 no. 36 14681-14686

A considerable body of previous research on the prefrontal cortex (PFC) has helped characterize the regional specificity of various cognitive functions, such as cognitive control and decision making. Here we provide definitive findings on this topic, using a neuropsychological approach that takes advantage of a unique dataset accrued over several decades. We applied voxel-based lesion-symptom mapping in 344 individuals with focal lesions (165 involving the PFC) who had been tested on a comprehensive battery of neuropsychological tasks. Two distinct functional-anatomical networks were revealed within the PFC: one associated with cognitive control (response inhibition, conflict monitoring, and switching), which included the dorsolateral prefrontal cortex and anterior cingulate cortex and a second associated with value-based decision-making, which included the orbitofrontal, ventromedial, and frontopolar cortex. Furthermore, cognitive control tasks shared a common performance factor related to set shifting that was linked to the rostral anterior cingulate cortex. By contrast, regions in the ventral PFC were required for decision-making. These findings provide detailed causal evidence for a remarkable functional-anatomical specificity in the human PFC.

Cooperation and assortativity with dynamic partner updating


Jing Wang, Siddharth Suri, and Duncan J. Watts
PNAS September 4, 2012 vol. 109 no. 36 14363-14368

The natural tendency for humans to make and break relationships is thought to facilitate the emergence of cooperation. In particular, allowing conditional cooperators to choose with whom they interact is believed to reinforce the rewards accruing to mutual cooperation while simultaneously excluding defectors. Here we report on a series of human subjects experiments in which groups of 24 participants played an iterated prisoner’s dilemma game where, critically, they were also allowed to propose and delete links to players of their own choosing at some variable rate. Over a wide variety of parameter settings and initial conditions, we found that dynamic partner updating significantly increased the level of cooperation, the average payoffs to players, and the assortativity between cooperators. Even relatively slow update rates were sufficient to produce large effects, while subsequent increases to the update rate had progressively smaller, but still positive, effects. For standard prisoner’s dilemma payoffs, we also found that assortativity resulted predominantly from cooperators avoiding defectors, not by severing ties with defecting partners, and that cooperation correspondingly suffered. Finally, by modifying the payoffs to satisfy two novel conditions, we found that cooperators did punish defectors by severing ties, leading to higher levels of cooperation that persisted for longer.