2012年3月29日木曜日

Neural responses to ingroup and outgroup members' suffering predict individual differences in costly helping.


Grit Hein, Giorgia Silani, Kerstin Preuschoff, C Daniel Batson, and Tania Singer
Neuron 2010 vol. 68 (1) pp. 149-160

他人の痛みを引き受けるか?他人が自分と同集団(同じサッカーチームのファン)に属するとき、引き受ける頻度が高く、その頻度の個人差は「『痛み受けている他人』を見ている際のInsula(島皮質)の活動」で説明できる。 http://www.ncbi.nlm.nih.gov/pubmed/20920798

Little is known about the neurobiological mechanisms underlying prosocial decisions and how they are modulated by social factors such as perceived group membership. The present study investigates the neural processes preceding the willingness to engage in costly helping toward ingroup and outgroup members. Soccer fans witnessed a fan of their favorite team (ingroup member) or of a rival team (outgroup member) experience pain. They were subsequently able to choose to help the other by enduring physical pain themselves to reduce the other's pain. Helping the ingroup member was best predicted by anterior insula activation when seeing him suffer and by associated self-reports of empathic concern. In contrast, not helping the outgroup member was best predicted by nucleus accumbens activation and the degree of negative evaluation of the other. We conclude that empathy-related insula activation can motivate costly helping, whereas an antagonistic signal in nucleus accumbens reduces the propensity to help.

Differential roles of fairness- and compassion-based motivations for cooperation, defection, and punishment.


Tania Singer and Nikolaus Steinbeis
Annals of the New York Academy of Sciences
2009 vol. 1167 pp. 41-50

【概要】
「公平性」に基づく協力と「同情・共感」に基づく協力の二種類があり、それぞれ違う脳部位が関与している。

【公平性に基づく協力】
「非協力者に罰を与える」という効果があるのではないか?
実際、実験ゲーム研究により、「人々は非協力者を罰する」、「罰を受ける可能性がある時、人々は協力する」ことが示されている。
また、近年の神経科学研究により、
・非協力者に罰を与える時、脳の報酬系(線条体:striatum)が活動する(de Quervain et al., Science 2004)→「罰を与える事自体が報酬として知覚されている」可能性、
・最後通牒ゲームで不公平な提案を拒否するのに前頭前野外背側部(dlPFC)が関与していること、
が示唆されている。

【同情・共感に基づく協力】
非協力者に罰を与えるだけでは、協力は達成できない。「間違えて(意図せず)協力に失敗した人を許す」ことが必要になる。同情・共感に基づく協力はこの「許す」ことに効いているのではないか(相手の事情を鑑みて、罰を与えるのを止める)?
神経基盤としては、
・島前部(anterior insula)、前帯状回(ACC)は「自分の痛み」にも「他人の痛み」にも反応することが知られている → 共感・同情の基盤である、
と示唆されている。

Separating value from choice: delay discounting activity in the lateral intraparietal area.


Kenway Louie and Paul W Glimcher
Journal of Neuroscience, 30(16), 5498–5507.

LIP neuronsは意思決定過程の前半は「選択肢の価値」、後半は「その選択確率」をコードしている。価値と選択確率を分離できる実験課題("価値の高い方を選ぶ"ので両者の分離は通常困難)がポイント。 http://www.jneurosci.org/content/30/16/5498

The mathematical formulations used to study the neurophysiological signals governing choice behavior fall under one of two major theoretical frameworks: "choice probability" or "subjective value." These two formulations represent behavioral quantities closely tied to the decision process, but it is unknown whether one of these variables, or both, dominates the neural mechanisms that mediate choice. Value and choice probability are difficult to distinguish in practice, because higher-valued options are chosen more frequently in free-choice tasks. This distinction is particularly relevant for sensorimotor areas such as parietal cortex, where both value information and motor signals related to choice have been observed. We recorded the activity of neurons in the lateral intraparietal area while monkeys performed an intertemporal choice task for rewards differing in delay to reinforcement. Here we show that the activity of parietal neurons is precisely correlated with the individual-specific discounted value of delayed rewards, with peak subjective value modulation occurring early in task trials. In contrast, late in the decision process these same neurons transition to encode the selected action. When directly compared, the strong delay-related modulation early during decision making is driven by subjective value rather than the monkey's probability of choice. These findings show that in addition to information about gains, parietal cortex also incorporates information about delay into a precise physiological correlate of economic value functions, independent of the probability of choice.

2012年3月27日火曜日

Contextual encoding by ensembles of medial prefrontal cortex neurons


James M. Hyman, Liya Ma, Emili Balaguer-Ballester, Daniel Durstewitz, and Jeremy K. Seamans
PNAS March 27, 2012 vol. 109 no. 13 5086-5091

Contextual representations serve to guide many aspects of behavior and influence the way stimuli or actions are encoded and interpreted. The medial prefrontal cortex (mPFC), including the anterior cingulate subregion, has been implicated in contextual encoding, yet the nature of contextual representations formed by the mPFC is unclear. Using multiple single-unit tetrode recordings in rats, we found that different activity patterns emerged in mPFC ensembles when animals moved between different environmental contexts. These differences in activity patterns were significantly larger than those observed for hippocampal ensembles. Whereas ≈11% of mPFC cells consistently preferred one environment over the other across multiple exposures to the same environments, optimal decoding (prediction) of the environmental setting occurred when the activity of up to ≈50% of all mPFC neurons was taken into account. On the other hand, population activity patterns were not identical upon repeated exposures to the very same environment. This was partly because the state of mPFC ensembles seemed to systematically shift with time, such that we could sometimes predict the change in ensemble state upon later reentry into one environment according to linear extrapolation from the time-dependent shifts observed during the first exposure. We also observed that many strongly action-selective mPFC neurons exhibited a significant degree of context-dependent modulation. These results highlight potential differences in contextual encoding schemes by the mPFC and hippocampus and suggest that the mPFC forms rich contextual representations that take into account not only sensory cues but also actions and time.

2012年3月20日火曜日

Incorporation of new information into prefrontal cortical activity after learning working memory tasks


Ethan M. Meyers, Xue-Lian Qi, and Christos Constantinidis
PNAS 2012 109 (12) 4651-4656.

The ability to learn new tasks requires that new information is integrated into neural systems that already support other behaviors. To study how new information is incorporated into neural representations, we analyzed single-unit recordings from the prefrontal cortex (PFC), a brain region important for task acquisition and working memory, before and after monkeys learned to perform two behavioral tasks. A population-decoding analysis revealed a large increase in task-relevant information, and smaller changes in stimulus-related information, after training. This new information was contained in dynamic patterns of neural activity, with many individual neurons containing the new task-relevant information for only relatively short periods of time in the midst of other large firing rate modulations. Additionally, we found that stimulus information could be decoded with high accuracy only from dorsal PFC, whereas task-relevant information was distributed throughout both dorsal and ventral PFC. These findings help resolve a controversy about whether PFC is innately specialized to process particular types of information or whether its responses are completely determined by task demands by showing there is both regional specialization within PFC that was present before training, as well as more widespread task-relevant information that is a direct result of learning. The results also show that information is incorporated into PFC through the emergence of a small population of highly selective neurons that overlay new signals on top of patterns of activity that contain information about previously encoded variables, which gives insight into how information is coded in neural activity.

Neuronal activity in the primate dorsomedial prefrontal cortex contributes to strategic selection of response tactics


Yoshiya Matsuzaka, Tetsuya Akiyama, Jun Tanji, and Hajime Mushiake
PNAS 2012 109 (12) 4633-4638.

The functional roles of the primate posterior medial prefrontal cortex have remained largely unknown. Here, we show that this region participates in the regulation of actions in the presence of multiple response tactics. Monkeys performed a forelimb task in which a visual cue required prompt decision of reaching to a left or a right target. The location of the cue was either ipsilateral (concordant) or contralateral (discordant) to the target. As a result of extensive training, the reaction times for the concordant and discordant trials were indistinguishable, indicating that the monkeys developed tactics to overcome the cue-response conflict. Prefrontal neurons exhibited prominent activity when the concordant and discordant trials were randomly presented, requiring rapid selection of a response tactic (reach toward or away from the cue). The following findings indicate that these neurons are involved in the selection of tactics, rather than the selection of action or monitoring of response conflict: (i) The response period activity of neurons in this region disappeared when the monkeys performed the task under the behavioral condition that required a single tactic alone, whereas the action varied across trials. (ii) The neuronal activity was found in the dorsomedial prefrontal cortex but not in the anterior cingulate cortex that has been implicated for the response conflict monitoring. These results suggest that the medial prefrontal cortex participates in the selection of a response tactic that determines an appropriate action. Furthermore, the observation of dynamic, task-dependent neuronal activity necessitates reconsideration of the conventional concept of cortical motor representation.

Lateral prefrontal cortex contributes to maladaptive decisions


PNAS 2012 109 (12) 4401-4406.
Gui Xue, Chi-Hung Juan, Chi-Fu Chang, Zhong-Lin Lu, and Qi Dong

ルーレットで「緑」が連続で出ると、「次は赤が出るだろう(ギャンブラーの誤り)」or「次も緑が出るだろう(強化学習)」と思う。前者には前頭前野外背側部、後者には大脳基底核・線条体が関与する。 http://www.pnas.org/content/109/12/4401 http://www.jneurosci.org/content/31/17/6296

Humans consistently make suboptimal decisions involving random events, yet the underlying neural mechanisms remain elusive. Using functional MRI and a matching pennies game that captured subjects’ increasing tendency to predict the break of a streak as it continued [i.e., the “gambler's fallacy” (GF)], we found that a strong blood oxygen level-dependent response in the left lateral prefrontal cortex (LPFC) to the current outcome preceded the use of the GF strategy 10 s later. Furthermore, anodal transcranial direct current stimulation over the left LPFC, which enhances neuronal firing rates and cerebral excitability, increased the use of the GF strategy, and made the decisions more “sticky.” These results reveal a causal role of the LPFC in implementing suboptimal decision strategy guided by false world models, especially when such strategy requires great resources for cognitive control.

2012年3月14日水曜日

Neuronal Encoding of Subjective Value in Dorsal and Ventral Anterior Cingulate Cortex


Xinying Cai and Camillo Padoa-Schioppa
J. Neurosci. 2012;32 3791-3808
http://www.jneurosci.org/cgi/content/abstract/32/11/3791?etoc

二種類のジュースから一つを選ぶ(サル電気生理)。前帯状皮質は「選ばれたジュース」の主観的価値をコードしている(一方、眼窩前頭皮質は「それぞれのジュースの価値」を保持)。前帯状皮質は意思決定過程の(運動制御に近い)下流に関与。 http://www.jneurosci.org/content/32/11/3791

We examined the activity of individual cells in the primate anterior cingulate cortex during an economic choice task. In the experiments, monkeys chose between different juices offered in variables amounts and subjective values were inferred from the animals' choices. We analyzed neuronal firing rates in relation to a large number of behaviorally relevant variables. We report three main results. First, there were robust differences between the dorsal bank (ACCd) and the ventral bank (ACCv) of the cingulate sulcus. Specifically, neurons in ACCd but not in ACCv were modulated by the movement direction. Furthermore, neurons in ACCd were most active before movement initiation, whereas neurons in ACCv were most active after juice delivery. Second, neurons in both areas encoded the identity and the subjective value of the juice chosen by the animal. In contrast, neither region encoded the value of individual offers. Third, the population of value-encoding neurons in both ACCd and ACCv underwent range adaptation. With respect to economic choice, it is interesting to compare these areas with the orbitofrontal cortex (OFC), previously examined. While neurons in OFC encoded both pre-decision and post-decision variables, neurons in ACCd and ACCv only encoded post-decision variables. Moreover, the encoding of the choice outcome (chosen value and chosen juice) in ACCd and ACCv trailed that found in OFC. These observations indicate that economic decisions (i.e., value comparisons) take place upstream of ACCd and ACCv. The coexistence of choice outcome and movement signals in ACCd suggests that this area constitutes a gateway through which the choice system informs motor systems.

Multisensory Decision-Making in Rats and Humans


David Raposo, John P. Sheppard, Paul R. Schrater, and Anne K. Churchland
J. Neurosci. 2012;32 3726-3735
http://www.jneurosci.org/cgi/content/abstract/32/11/3726?etoc

We report a novel multisensory decision task designed to encourage subjects to combine information across both time and sensory modalities. We presented subjects, humans and rats, with multisensory event streams, consisting of a series of brief auditory and/or visual events. Subjects made judgments about whether the event rate of these streams was high or low. We have three main findings. First, we report that subjects can combine multisensory information over time to improve judgments about whether a fluctuating rate is high or low. Importantly, the improvement we observed was frequently close to, or better than, the statistically optimal prediction. Second, we found that subjects showed a clear multisensory enhancement both when the inputs in each modality were redundant and when they provided independent evidence about the rate. This latter finding suggests a model where event rates are estimated separately for each modality and fused at a later stage. Finally, because a similar multisensory enhancement was observed in both humans and rats, we conclude that the ability to optimally exploit sequentially presented multisensory information is not restricted to a particular species.

The Cost of Accumulating Evidence in Perceptual Decision Making


Jan Drugowitsch, Ruben Moreno-Bote, Anne K. Churchland, Michael N. Shadlen,
and Alexandre Pouget
J. Neurosci. 2012;32 3612-3628
http://www.jneurosci.org/cgi/content/abstract/32/11/3612?etoc

Decision making often involves the accumulation of information over time, but acquiring information typically comes at a cost. Little is known about the cost incurred by animals and humans for acquiring additional information from sensory variables due, for instance, to attentional efforts. Through a novel integration of diffusion models and dynamic programming, we were able to estimate the cost of making additional observations per unit of time from two monkeys and six humans in a reaction time (RT) random-dot motion discrimination task. Surprisingly, we find that the cost is neither zero nor constant over time, but for the animals and humans features a brief period in which it is constant but increases thereafter. In addition, we show that our theory accurately matches the observed reaction time distributions for each stimulus condition, the time-dependent choice accuracy both conditional on stimulus strength and independent of it, and choice accuracy and mean reaction times as a function of stimulus strength. The theory also correctly predicts that urgency signals in the brain should be independent of the difficulty, or stimulus strength, at each trial.

2012年3月13日火曜日

Adaptive coding of reward prediction errors is gated by striatal coupling


Soyoung Q. Park, Thorsten Kahnt, Deborah Talmi, Jörg Rieskamp, Raymond J. Dolan, and Hauke R. Heekeren
PNAS March 13, 2012 vol. 109 no. 11 4285-4289

To efficiently represent all of the possible rewards in the world, dopaminergic midbrain neurons dynamically adapt their coding range to the momentarily available rewards. Specifically, these neurons increase their activity for an outcome that is better than expected and decrease it for an outcome worse than expected, independent of the absolute reward magnitude. Although this adaptive coding is well documented, it remains unknown how this rescaling is implemented. To investigate the adaptive coding of prediction errors and its underlying rescaling process, we used human functional magnetic resonance imaging (fMRI) in combination with a reward prediction task that involved different reward magnitudes. We demonstrate that reward prediction errors in the human striatum are expressed according to an adaptive coding scheme. Strikingly, we show that adaptive coding is gated by changes in effective connectivity between the striatum and other reward-sensitive regions, namely the midbrain and the medial prefrontal cortex. Our results provide evidence that striatal prediction errors are normalized by a magnitude-dependent alteration in the interregional connectivity within the brain's reward system.

2012年3月10日土曜日

震災から一年


今日で東日本大震災から一年ですね。
節目に新たにできることは特にないですが、これからも「忘れないこと」、「些細でも支援をすること」を続けて行きたいなと思います*。

個人的には、とりあえず、「インパクト・ファクター募金(論文がアクセプトされたら、IF×1万円を募金する)」をたくさんできるよう研究をがんばります。

* 阪神大震災の場合、ぼくが通っていた高校の校庭の半分は5年間仮設住宅でした。幼馴染みが元のマンションに復帰できたのは四年半後です。今でも難しい状況に置かれている人が大勢いるでしょう。

ランチ@銀座 岡半(贅沢で幸せなお肉)


休日のランチは贅沢に銀座・岡半へ。
http://r.gnavi.co.jp/g080500/
http://r.tabelog.com/tokyo/A1301/A130101/13002562/dtlrvwlst/781674/
言わずとしれた鉄板焼き・すき焼き・しゃぶしゃぶの名店、味も値段も一流です。
(いつかディナーで行ってみたい!誰か奢って…:笑)

オーダーしたのはランチの名物「和牛リブロース薄焼」。

さらに贅沢して1.5人前、1900円。
柔らかくて絶品。
鉄板の前に座ってシェフが自ら焼いてくれます。
コテさばきが芸術的で感動!
肉だけでなく、ソースや余分な油といった液体をコテで見事に捌いていく姿に惚れた。

付け合わせは、ハンバーグ入りシチューと赤出汁。
シチューはあつあつで、トロける玉葱がおいしかったです。
(赤出汁は濃いめでちょっと喉乾くけどね)

最後は別室で「お」抹茶を頂いて終了。
(贅沢なランチだったので贅沢に「お」を付けてみた)

相変わらず、期待を裏切らない味で美味しかったです。
(再掲 → 今度はディナーで行ってみたい誰か奢って…:笑)

2012年3月7日水曜日

Impulse Control and Underlying Functions of the Left DLPFC Mediate Age-Related and Age-Independent Individual Differences in Strategic Social Behavior


Nikolaus Steinbeis, Boris C. Bernhardt, Tania Singer
Neuron, Volume 73, Issue 5, 1040-1051, 8 March 2012


戦略的行動の発達とその神経基盤。7-14歳の子供がMRI中で最後通牒ゲームと独裁者ゲームを行う。戦略的行動(両ゲームでの提案額の差)は年齢と正の相関があり、前頭前野外背側部(dlPFC)の活動及び大きさ(厚さ)で説明できる。 http://www.sciencedirect.com/science/article/pii/S0896627312000773

子供のfMRIも珍しいけど、行動データが面白い。戦略的行動の発達は公平性評価や他者信念予測能力では説明できないが、衝動性制御能力で説明できる。つまり、子供が戦略的に行動できないのは社会規範や他者の心を読めないからでなく、短期的利益追求の衝動を制御できないからである。


Human social exchange is often characterized by conflicts of interest requiring strategic behavior for their resolution. To investigate the development of the cognitive and neural mechanisms underlying strategic behavior, we studied children's decisions while they played two types of economic exchange games with differing demands of strategic behavior. We show an increase of strategic behavior with age, which could not be explained by age-related changes in social preferences but instead by developmental differences in impulsivity and associated brain functions of the left dorsolateral prefrontal cortex (DLPFC). Furthermore, observed differences in cortical thickness of lDLPFC were predictive of differences in impulsivity and strategic behavior irrespective of age. We conclude that egoistic behavior in younger children is not caused by a lack of understanding right or wrong, but by the inability to implement behavioral control when tempted to act selfishly; a function relying on brain regions maturing only late in ontogeny.

Dissociating Modality-Specific and Supramodal Neural Systems for Action Understanding


Robert P. Spunt and Matthew D. Lieberman
J. Neurosci. 2012;32 3575-3583
http://www.jneurosci.org/cgi/content/abstract/32/10/3575?etoc

他者行動の「やり方」と「目的」を理解する際の神経活動。前者には頭頂葉を中心としたミラーニューロン・システムが関与し、後者には前頭前野内側部を中心とした心の理論システムが関与する。 http://www.jneurosci.org/content/32/10/3575

The neural basis of action understanding in humans remains disputed, with some research implicating the putative mirror neuron system (MNS) and some a mentalizing system (MZS) for inferring mental states. The basis for this dispute may be that action understanding is a heterogeneous construct: actions can be understood from sensory information about body movements or from language about action, and with the goal of understanding the implementation (“how”) or motive (“why”) of an action. Although extant research implicates the MNS in understanding implementation and the MZS in understanding motive, it remains unknown to what extent these systems subserve modality-specific or supramodal functions in action understanding. While undergoing fMRI, 21 volunteers considered the implementation (“How is she doing it?”) and motive (“Why is she doing it?”) for actions presented in video or text. Bilateral parietal and right frontal areas of the MNS showed a modality-specific association with perceiving actions in videos, while left-hemisphere MNS showed a supramodal association with understanding implementation. Largely left-hemisphere MZS showed a supramodal association with understanding motive; however, connectivity among the MZS and MNS during the inference of motive was modality specific, being significantly stronger when motive was understood from actions in videos compared to text. These results support a tripartite model of MNS and MZS contributions to action understanding, where distinct areas of the MNS contribute to action perception (“perceiving what”) and the representation of action implementation (“knowing how”), while the MZS supports an abstract, modality-independent representation of the mental states that explain action performance (“knowing why”).