2012年6月27日水曜日

Social Network Modulation of Reward-Related Signals


Dominic S. Fareri, Michael A. Niznikiewicz, Victoria K. Lee, and Mauricio R. Delgado
J. Neurosci. 2012;32 9045-9052
http://www.jneurosci.org/cgi/content/abstract/32/26/9045?etoc

ヒトfMRI。赤の他人と報酬を分け合うより、友人と分け合った方が嬉しい(赤の他人でもコンピュータと分け合うよりは嬉しい)。その「嬉しさの違い」は腹側線条体にコードされている。 http://www.jneurosci.org/content/32/26/9045

Everyday goals and experiences are often shared with others who may hold different places within our social networks. We investigated whether the experience of sharing a reward differs with respect to social network. Twenty human participants played a card guessing game for shared monetary outcomes with three partners: a computer, a confederate (out of network), and a friend (in network). Participants subjectively rated the experience of sharing a reward more positively with their friends than the other partners. Neuroimaging results support participants' subjective reports, as ventral striatal BOLD responses were more robust when sharing monetary gains with a friend as compared to the confederate or computer, suggesting a higher value for sharing with an in-network partner. Interestingly, ratings of social closeness covaried with this activity, resulting in a significant partner × closeness interaction; exploratory analysis showed that only participants reporting higher levels of closeness demonstrated partner-related differences in striatal BOLD response. These results suggest that reward valuation in social contexts is sensitive to distinctions of social network, such that sharing positive experiences with in-network others may carry higher value.

Threat of Punishment Motivates Memory Encoding via Amygdala, Not Midbrain, Interactions with the Medial Temporal Lobe


Vishnu P. Murty, Kevin S. LaBar, and R. Alison Adcock
J. Neurosci. 2012;32 8969-8976
http://www.jneurosci.org/cgi/content/abstract/32/26/8969?etoc

Neural circuits associated with motivated declarative encoding and active threat avoidance have both been described, but the relative contribution of these systems to punishment-motivated encoding remains unknown. The current study used functional magnetic resonance imaging in humans to examine mechanisms of declarative memory enhancement when subjects were motivated to avoid punishments that were contingent on forgetting. A motivational cue on each trial informed participants whether they would be punished or not for forgetting an upcoming scene image. Items associated with the threat of shock were better recognized 24 h later. Punishment-motivated enhancements in subsequent memory were associated with anticipatory activation of right amygdala and increases in its functional connectivity with parahippocampal and orbitofrontal cortices. On a trial-by-trial basis, right amygdala activation during the motivational cue predicted hippocampal activation during encoding of the subsequent scene; across participants, the strength of this interaction predicted memory advantages due to motivation. Of note, punishment-motivated learning was not associated with activation of dopaminergic midbrain, as would be predicted by valence-independent models of motivation to learn. These data are consistent with the view that motivation by punishment activates the amygdala, which in turn prepares the medial temporal lobe for memory formation. The findings further suggest a brain system for declarative learning motivated by punishment that is distinct from that for learning motivated by reward.

2012年6月20日水曜日

Anterior Prefrontal Cortex Contributes to Action Selection through Tracking of Recent Reward Trends


Christopher K. Kovach, Nathaniel D. Daw, David Rudrauf, Daniel Tranel, John
P. O'Doherty, and Ralph Adolphs
J. Neurosci. 2012;32 8434-8442
http://www.jneurosci.org/cgi/content/abstract/32/25/8434?etoc

ヒト損傷研究。被験者は四つの選択肢(それぞれの価値は時間的に変動する)から一つを選ぶ。健常者と違って、前頭極・損傷患者は価値の変動傾向を予測しない(単に強化学習的に価値を更新)。つまり、前頭極は「価値の変動傾向の予測」を司っている。

The functions of prefrontal cortex remain enigmatic, especially for its anterior sectors, putatively ranging from planning to self-initiated behavior, social cognition, task switching, and memory. A predominant current theory regarding the most anterior sector, the frontopolar cortex (FPC), is that it is involved in exploring alternative courses of action, but the detailed causal mechanisms remain unknown. Here we investigated this issue using the lesion method, together with a novel model-based analysis. Eight patients with anterior prefrontal brain lesions including the FPC performed a four-armed bandit task known from neuroimaging studies to activate the FPC. Model-based analyses of learning demonstrated a selective deficit in the ability to extrapolate the most recent trend, despite an intact general ability to learn from past rewards. Whereas both brain-damaged and healthy controls used comparisons between the two most recent choice outcomes to infer trends that influenced their decision about the next choice, the group with anterior prefrontal lesions showed a complete absence of this component and instead based their choice entirely on the cumulative reward history. Given that the FPC is thought to be the most evolutionarily recent expansion of primate prefrontal cortex, we suggest that its function may reflect uniquely human adaptations to select and update models of reward contingency in dynamic environments.

Neuron誌から論文が出版!


今の職場に来てからの論文がやっとNeuron誌から出版されました!

"Learning to Simulate Others' Decisions"
Shinsuke Suzuki, Norihiro Harasawa, Kenichi Ueno, Justin L. Gardner, Noritaka Ichinohe, Masahiko Haruno, Kang Cheng, Hiroyuki Nakahara.
Neuron, Volume 74, Issue 6, 1125-1137, 21 June 2012

fMRIと機械学習を組み合わせることで、ヒト(の脳)が「シミュレーションによる学習」と「他人の行動観察による学習」を統合して「他人の価値観・意思決定プロセスを学ぶ」ことを明らかにしました。

詳しい内容は下記をご覧下さい:
論文(英語:プロ向け)
http://www.cell.com/neuron/abstract/S0896-6273(12)00427-8
プレスリリース(日本語:一般向け)
http://www.riken.jp/r-world/info/release/press/2012/120621/index.html
http://www.riken.jp/r-world/info/release/press/2012/120621/detail.html

投稿からアクセプトまでは難産ではなかったのですが、トータルで長かった…
最後にこれまでの経緯をまとめておきます。
四年間の努力が「Neuron誌からの出版」という形で報われて、正直ホッとしています。

同業者の皆様へ、
よろしければ、ぜひ論文を引用してやって下さい。
かしこ。

-------------
2008年4月:現職場に着任。
2008年4月-2009年3月:倫理委員会への研究計画申請やfMRI使用法の勉強。
同時に、実験計画を考えて、ボスと大まかな結論に達したのが年度末。
2009年4月-10月:半年かけて、実験課題の詰めや予備実験を実施。
2009年11月-2010年7月:fMRI実験。来る日も来る日も実験(と基本的なデータ解析)。
2010年8月-12月:実験データを解析・メインのストーリーを決定。年末には論文第一稿をボスに提出。
2011年1月-7月:原稿の改訂・追加実験も。
2011年7月:論文をNeuron誌に投稿。
2011年9月:査読結果到着。結果は「Major Revision」…
査読者1「ややポジティブ」、査読者2「超ネガティブ(ボロクソ言われました…)」、査読者3「超ポジティブ(ベタ誉め)」という結果で、なんとかリジェクトは免れる。
2011年9-12月:再投稿に向けて、追加実験、データ再解析、論文改訂。
2012月1月:再投稿。
2012年4月:アクセプト!
結局、二回目の査読は査読者1と3にだけまわった模様。二人とも「掲載OK」ということで、無事アクセプトに。

2012年6月19日火曜日

Direct reciprocity in structured populations


Matthijs van Veelen, Julián García, David G. Rand, and Martin A. Nowak
PNAS June 19, 2012 vol. 109 no. 25 9929-9934

Reciprocity and repeated games have been at the center of attention when studying the evolution of human cooperation. Direct reciprocity is considered to be a powerful mechanism for the evolution of cooperation, and it is generally assumed that it can lead to high levels of cooperation. Here we explore an open-ended, infinite strategy space, where every strategy that can be encoded by a finite state automaton is a possible mutant. Surprisingly, we find that direct reciprocity alone does not lead to high levels of cooperation. Instead we observe perpetual oscillations between cooperation and defection, with defection being substantially more frequent than cooperation. The reason for this is that “indirect invasions” remove equilibrium strategies: every strategy has neutral mutants, which in turn can be invaded by other strategies. However, reciprocity is not the only way to promote cooperation. Another mechanism for the evolution of cooperation, which has received as much attention, is assortment because of population structure. Here we develop a theory that allows us to study the synergistic interaction between direct reciprocity and assortment. This framework is particularly well suited for understanding human interactions, which are typically repeated and occur in relatively fluid but not unstructured populations. We show that if repeated games are combined with only a small amount of assortment, then natural selection favors the behavior typically observed among humans: high levels of cooperation implemented using conditional strategies.

Dissociating activity in the lateral intraparietal area from value using a visual foraging task


Koorosh Mirpour and James W. Bisley
PNAS June 19, 2012 vol. 109 no. 25 10083-10088

We make decisions about where to look approximately three times per second in normal viewing. It has been suggested that eye movements may be guided by activity in the lateral intraparietal area (LIP), which is thought to represent the relative value of objects in space. However, it is not clear how values for saccade goal selection are prioritized while free-viewing in a cluttered visual environment. To address this question, we compared the neural responses of LIP neurons in two subjects with their saccadic behavior and three estimates of stimulus value. These measures were extracted from the subjects’ performance in a visual foraging task, in which we parametrically controlled the number of objects on the screen. We found that the firing rates of LIP neurons did not correlate well with the animals’ behavior or any of our estimated measures of value. However, if the LIP activity was further normalized, it became highly correlated with the animals’ decisions. These data suggest that LIP activity does not represent value in complex environments, but that the value can easily be extracted with one further step of processing. We propose that activity in LIP represents attentional priority and that the downstream normalization of this activity is an essential process in guiding action.

2012年6月16日土曜日

地元の隠れた名店「うどん処 おはな」


我が街(まだ4年しか住んでないけど…:笑)の隠れた名店「うどん処 おはな」。
http://r.tabelog.com/saitama/A1103/A110301/11022150/

平日ランチはほぼ毎日社食でうどんを食べる私が、さらに休日にも、うどんを食べに行ってしまうほど美味しいお店。
先日訪問した東京・大阪の有名店「つるとんたん」を余裕で超える味です。
都心にあったら、サラリーマン・OLがランチに、飲み会の締めに、殺到する事間違いなしです。
本当に最高。まさに至高の味です。

さて、メニューですが、お薦めは「おはなうどん」と「つけカレーうどん」。
どちらもランチでは炊き込みご飯がついてきます(はい、鉄板の組み合わせですね)。

まずは定番「おはなうどん」。
コシの強い太めの「うどん」に、甘く味つけられた「きつね」。
ダシの効いた「おつゆ」。トドメは甘辛く煮付けられた「牛肉」。
あと、「わかめ」と「えび天」は普通。
全体的にとても良くまとまっていて優しい味です。
なんか関西人のDNAに沁みますね。故郷を思い出します。

そして最近のマイ・ブーム「つけカレーうどん」。
「カレーうどん」は日本人が行った最も偉大な発明の一つだと確信しているのですが(だって、「カレー」+「うどん」ですよ!)、その中でもここのは秀逸です。
香辛料の効いたピリ辛のカレーつけ汁に太めのうどんがよく合います。
インド人のDNAに沁みますね(知らんけど:笑)。
うどん玉だけ持ってインド行きたい!


というわけで、「うどん処 おはな」!
今日も行ってきます!

2012年6月13日水曜日

Time-Dependent Changes in Human Corticospinal Excitability Reveal Value-Based Competition for Action during Decision Processing


Miriam Cornelia Klein-Flugge and Sven Bestmann
J. Neurosci. 2012;32 8373-8382
http://www.jneurosci.org/cgi/content/abstract/32/24/8373?etoc

Our choices often require appropriate actions to obtain a preferred outcome, but the neural underpinnings that link decision making and action selection remain largely undetermined. Recent theories propose that action selection occurs simultaneously, i.e., parallel in time, with the decision process. Specifically, it is thought that action selection in motor regions originates from a competitive process that is gradually biased by evidence signals originating in other regions, such as those specialized in value computations. Biases reflecting the evaluation of choice options should thus emerge in the motor system before the decision process is complete. Using transcranial magnetic stimulation, we sought direct physiological evidence for this prediction by measuring changes in corticospinal excitability in human motor cortex during value-based decisions. We found that excitability for chosen versus unchosen actions distinguishes the forthcoming choice before completion of the decision process. Both excitability and reaction times varied as a function of the subjective value-difference between chosen and unchosen actions, consistent with this effect being value-driven. This relationship was not observed in the absence of a decision. Our data provide novel evidence in humans that internally generated value-based decisions influence the competition between action representations in motor cortex before the decision process is complete. This is incompatible with models of serial processing of stimulus, decision, and action.

Neural Correlates of Specific and General Pavlovian-to-Instrumental Transfer within Human Amygdalar Subregions: A High-Resolution fMRI Study


Charlotte Prevost, Mimi Liljeholm, Julian M. Tyszka, and John P. O'Doherty
J. Neurosci. 2012;32 8383-8390
http://www.jneurosci.org/cgi/content/abstract/32/24/8383?etoc

It is widely held that the interaction between instrumental and Pavlovian conditioning induces powerful motivational biases. Pavlovian-Instrumental Transfer (PIT) is one of the key paradigms demonstrating this effect, which can further be decomposed into a general and specific component. Although these two forms of PIT have been studied at the level of amygdalar subregions in rodents, it is still unknown whether they involve different areas of the human amygdala. Using a high-resolution fMRI (hr-fMRI) protocol optimized for the amygdala in combination with a novel free operant task designed to elicit effects of both general and specific PIT, we demonstrate that a region of ventral amygdala within the boundaries of the basolateral complex and the ventrolateral putamen are involved in specific PIT, while a region of dorsal amygdala within the boundaries of the centromedial complex is involved in general PIT. These results add to a burgeoning literature indicating different functional contributions for these different amygdalar subregions in reward-processing and motivation.

2012年6月12日火曜日

Emotions promote social interaction by synchronizing brain activity across individuals


Lauri Nummenmaa, Enrico Glerean, Mikko Viinikainen, Iiro P. Jääskeläinen, Riitta Hari, and Mikko Sams
PNAS June 12, 2012 vol. 109 no. 24 9599-9604

Sharing others’ emotional states may facilitate understanding their intentions and actions. Here we show that networks of brain areas “tick together” in participants who are viewing similar emotional events in a movie. Participants’ brain activity was measured with functional MRI while they watched movies depicting unpleasant, neutral, and pleasant emotions. After scanning, participants watched the movies again and continuously rated their experience of pleasantness–unpleasantness (i.e., valence) and of arousal–calmness. Pearson’s correlation coefficient was used to derive multisubject voxelwise similarity measures [intersubject correlations (ISCs)] of functional MRI data. Valence and arousal time series were used to predict the moment-to-moment ISCs computed using a 17-s moving average. During movie viewing, participants' brain activity was synchronized in lower- and higher-order sensory areas and in corticolimbic emotion circuits. Negative valence was associated with increased ISC in the emotion-processing network (thalamus, ventral striatum, insula) and in the default-mode network (precuneus, temporoparietal junction, medial prefrontal cortex, posterior superior temporal sulcus). High arousal was associated with increased ISC in the somatosensory cortices and visual and dorsal attention networks comprising the visual cortex, bilateral intraparietal sulci, and frontal eye fields. Seed-voxel–based correlation analysis confirmed that these sets of regions constitute dissociable, functional networks. We propose that negative valence synchronizes individuals’ brain areas supporting emotional sensations and understanding of another’s actions, whereas high arousal directs individuals’ attention to similar features of the environment. By enhancing the synchrony of brain activity across individuals, emotions may promote social interaction and facilitate interpersonal understanding.

Salience driven value integration explains decision biases and preference reversal


Konstantinos Tsetsos, Nick Chater, and Marius Usher
PNAS June 12, 2012 vol. 109 no. 24 9659-9664

報酬に関する複数の情報を組み合わせて意思決定を行う。それぞれの情報のsaliency(顕著性?)を変えると、「選好の逆転」が起こる。行動経済学で見られる「意思決定のアノマリー」の原因は「複数の報酬情報を統合する過程」にあるのでは。

Human choice behavior exhibits many paradoxical and challenging patterns. Traditional explanations focus on how values are represented, but little is known about how values are integrated. Here we outline a psychophysical task for value integration that can be used as a window on high-level, multiattribute decisions. Participants choose between alternative rapidly presented streams of numerical values. By controlling the temporal distribution of the values, we demonstrate that this process underlies many puzzling choice paradoxes, such as temporal, risk, and framing biases, as well as preference reversals. These phenomena can be explained by a simple mechanism based on the integration of values, weighted by their salience. The salience of a sampled value depends on its temporal order and momentary rank in the decision context, whereas the direction of the weighting is determined by the task framing. We show that many known choice anomalies may arise from the microstructure of the value integration process.

2012年6月6日水曜日

Action Selection and Action Value in Frontal-Striatal Circuits


Moonsang Seo, Eunjeong Lee, Bruno B. Averbeck
Neuron, Volume 74, Issue 5, 947-960, 7 June 2012

サル電気生理。前頭前野と線条体はどちらも「行動の価値」や「行動選択」に関係すると言われていたが、実は、行動価値は主に(背側)線条体にコードされ、行動選択は主に(外側)前頭前野で行われている。

The role that frontal-striatal circuits play in normal behavior remains unclear. Two of the leading hypotheses suggest that these circuits are important for action selection or reinforcement learning. To examine these hypotheses, we carried out an experiment in which monkeys had to select actions in two different task conditions. In the first (random) condition, actions were selected on the basis of perceptual inference. In the second (fixed) condition, the animals used reinforcement from previous trials to select actions. Examination of neural activity showed that the representation of the selected action was stronger in lateral prefrontal cortex (lPFC), and occurred earlier in the lPFC than it did in the dorsal striatum (dSTR). In contrast to this, the representation of action values, in both the random and fixed conditions, was stronger in the dSTR. Thus, the dSTR contains an enriched representation of action value, but it followed frontal cortex in action selection.