2012年1月31日火曜日

Voodoo Correlation in Social Neuroscience


Twitterからの転載:

話題のVoodoo論文。前作もそうだったけど「Circular Analysis」と「多重比較」の話が混ざっていて読みにくい。社会神経科学における「神経活動と行動指標の被験者間相関」が槍玉に挙げられているけど… http://www.sciencedirect.com/science/article/pii/S1053811912000444

「データXに対して解析aを行ってROIを決め、同じデータのそのROIを対象に類似の解析a'を行う(Circular Analysis)」のはダメだけど、「同じデータXのそのROIを対象に独立な解析bを行う」のはあり?

多くの社会神経科学論文では、「被験者内比較でROIを決め、その活動の個人差が行動指標の個人差を説明できるか?」という問いを立てている。被験者内相関と被験者間相関に(論理的な)関係はないので、「(同じデータXを使っているけど)Circular Analysisなので完全にアウト!」とまでは言えないのでは…

社会神経科学論文でみられるもう一つのやり方としては「行動指標と被験者間で相関する部位を『全脳』から探す」というのもあるけど、こっちは明らかに(fMRI業界で昔から議論されてきた)多重比較補正の問題で、あえて「Voodoo」とか言う必要もない気がする。

ということを社会神経科学の側から考えてみた。一方、「Circular Analysis」とか「多重比較」といった問題に敏感にならないといけないのはその通りだと思うし、学際的な分野であるだけに基本が疎かになっている所はあるのかもしれない(と自戒を込めて)。

Dissociable neural representations of reinforcement and belief prediction errors underlie strategic learning


Lusha Zhu, Kyle E. Mathewson, and Ming Hsu
PNAS January 31, 2012 vol. 109 no. 5 1419-1424

Decision-making in the presence of other competitive intelligent agents is fundamental for social and economic behavior. Such decisions require agents to behave strategically, where in addition to learning about the rewards and punishments available in the environment, they also need to anticipate and respond to actions of others competing for the same rewards. However, whereas we know much about strategic learning at both theoretical and behavioral levels, we know relatively little about the underlying neural mechanisms. Here, we show using a multi-strategy competitive learning paradigm that strategic choices can be characterized by extending the reinforcement learning (RL) framework to incorporate agents’ beliefs about the actions of their opponents. Furthermore, using this characterization to generate putative internal values, we used model-based functional magnetic resonance imaging to investigate neural computations underlying strategic learning. We found that the distinct notions of prediction errors derived from our computational model are processed in a partially overlapping but distinct set of brain regions. Specifically, we found that the RL prediction error was correlated with activity in the ventral striatum. In contrast, activity in the ventral striatum, as well as the rostral anterior cingulate (rACC), was correlated with a previously uncharacterized belief-based prediction error. Furthermore, activity in rACC reflected individual differences in degree of engagement in belief learning. These results suggest a model of strategic behavior where learning arises from interaction of dissociable reinforcement and belief-based inputs.

2012年1月26日木曜日

Social networks and cooperation in hunter-gatherers


Coren L. Apicella, Frank W. Marlowe, James H. Fowler & Nicholas A. Christakis
Nature 481, 497–501 (26 January 2012)

Social networks show striking structural regularities1, 2, and both theory and evidence suggest that networks may have facilitated the development of large-scale cooperation in humans3, 4, 5, 6, 7. Here, we characterize the social networks of the Hadza, a population of hunter-gatherers in Tanzania8. We show that Hadza networks have important properties also seen in modernized social networks, including a skewed degree distribution, degree assortativity, transitivity, reciprocity, geographic decay and homophily. We demonstrate that Hadza camps exhibit high between-group and low within-group variation in public goods game donations. Network ties are also more likely between people who give the same amount, and the similarity in cooperative behaviour extends up to two degrees of separation. Social distance appears to be as important as genetic relatedness and physical proximity in explaining assortativity in cooperation. Our results suggest that certain elements of social network structure may have been present at an early point in human history. Also, early humans may have formed ties with both kin and non-kin, based in part on their tendency to cooperate. Social networks may thus have contributed to the emergence of cooperation.

2012年1月19日木曜日

Learning Acts on Distinct Processes for Visual Form Perception in the Human Brain


Stephen D. Mayhew, Sheng Li, and Zoe Kourtzi
The Journal of Neuroscience, 18 January 2012, 32(3):775-786;

Learning is known to facilitate our ability to detect targets in clutter and optimize brain processes for successful visual recognition. Previous brain-imaging studies have focused on identifying spatial patterns (i.e., brain areas) that change with learning, implicating occipitotemporal and frontoparietal areas. However, little is known about the interactions within this network that mediate learning-dependent improvement in complex perceptual tasks (i.e., discrimination of visual forms in clutter). Here we take advantage of the complementary high spatial and temporal resolution of simultaneous EEG-fMRI to identify the learning-dependent changes in spatiotemporal brain patterns that mediate enhanced behavioral sensitivity in the discrimination of global forms after training. We measured the observers' choices when discriminating between concentric and radial patterns presented in noise before and after training. Similarly, we measured the choices of a pattern classifier when predicting each stimulus from EEG-fMRI signals. By comparing the performance of human observers and classifiers, we demonstrated that learning alters sensitivity to visual forms and EEG-fMRI activation patterns related to distinct visual recognition processes. In particular, behavioral improvement after training was associated with changes in (1) early processes involved in the integration of global forms in higher occipitotemporal and parietal areas, and (2) later processes related to categorical judgments in frontal circuits. Thus, our findings provide evidence that learning acts on distinct visual recognition processes and shapes feedforward interactions across brain areas to support performance in complex perceptual tasks.

Amygdala Central Nucleus Interacts with Dorsolateral Striatum to Regulate the Acquisition of Habits


Nura W. Lingawi and Bernard W. Balleine
The Journal of Neuroscience, 18 January 2012, 32(3):1073-1081;

The role of the amygdala central nucleus (CeN) in habit learning was assessed in two experiments. First, we examined the effects of bilateral lesions of the anterior CeN on an overtraining-induced lever press habit evaluated using an outcome devaluation protocol. Overtraining generated habitual performance and rendered sham lesioned rats insensitive to outcome devaluation, an effect that was also found in rats given control lesions of the posterior CeN. In contrast, rats with lesions of the anterior CeN did not show normal habit acquisition and their performance remained goal-directed and sensitive to outcome devaluation. Nevertheless, lesions of either the posterior or the anterior CeN abolished the general excitatory influence of a Pavlovian conditioned stimulus on instrumental performance. Second, we assessed the functional interaction between the CeN and dorsolateral striatum (DLS), a region previously implicated in the acquisition of habits, using asymmetrical lesions to disconnect these structures. Rats were given a unilateral lesion of anterior CeN and a unilateral lesion of the DLS, made either ipsilateral (control) or contralateral (disconnection) to the CeN lesion, and given overtraining followed by outcome devaluation. Although the ipsilateral lesioned rats were insensitive to devaluation, the contralateral CeN–DLS lesion impaired habit acquisition, rendering performance sensitive to the devaluation treatment. These results are the first to implicate the CeN and its connection with a circuit involving DLS in habit learning. They imply that, in instrumental conditioning, regions of amygdala parse the instrumental outcome into the reward and reinforcement signals mediating goal-directed and habitual actions, respectively.

Inhaled oxytocin amplifies both vicarious reinforcement and self reinforcement in rhesus macaques (Macaca mulatta)


Steve W C Chang, Joseph W Barter, R Becket Ebitz, Karli K Watson, and Michael L Platt
PNAS
January 17, 2012
vol. 109, no. 3, 959–964

People attend not only to their own experiences, but also to the experiences of those around them. Such social awareness profoundly influences human behavior by enabling observational learning, as well as by motivating cooperation, charity, empathy, and spite. Oxytocin (OT), a neurosecretory hormone synthesized by hypothalamic neurons in the mammalian brain, can enhance affiliation or boost exclusion in different species in distinct contexts, belying any simple mechanistic neural model. Here we show that inhaled OT penetrates the CNS and subsequently enhances the sensitivity of rhesus macaques to rewards occurring to others as well as themselves. Roughly 2 h after inhaling OT, monkeys increased the frequency of prosocial choices associated with reward to another monkey when the alternative was to reward no one. OT also increased attention to the recipient monkey as well as the time it took to render such a decision. In contrast, within the first 2 h following inhalation, OT increased selfish choices associated with delivery of reward to self over a reward to the other monkey, without affecting attention or decision latency. Despite the differences in species typical social behavior, exogenous, inhaled OT causally promotes social donation behavior in rhesus monkeys, as it does in more egalitarian and monogamous ones, like prairie voles and humans, when there is no perceived cost to self. These findings potentially implicate shared neural mechanisms.

2012年1月16日月曜日

阪神大震災、17年目の17日


今日2011年1月17日で阪神大震災から17年目です。
今年も5時46分に黙祷することができました(もちろん二度寝しましたけどw)。


当時、中学生だったぼくや友人達は周りの大人や全国・全世界の色々な人に助けられました。コンビニが店舗を開放していたこと、近所の家に井戸水を貰いに行ったこと、学校では毎週のように炊き出しや文房具の寄付があったのを覚えています。もちろん他にも数えきれないくらいありました。今日は、「支援への感謝」と「東北やこれから起こる災害の被災者のために何ができるか」を改めて考える一日にしたいです。


また、17年の月日が流れ、自分自身も30歳を越えて友人達にも子どもが生まれたりで次の世代を意識するようになり、「震災を伝える」ことの重要性も最近意識できるようになりました。

・「震災時の食を考えるきっかけに」 宝塚市、避難所献立で給食
http://mainichi.jp/area/hyogo/news/20120106ddlk28040292000c.html
・三陸の津波後に建てられる石碑類について NHKの2006年番組から聞き書き
http://parasiteeve2.blog65.fc2.com/blog-entry-614.html

ぼくは1999年に高校を卒業して、兵庫県西宮市を出て関東に来ました。
当時は高校のグランドの半分は仮設住宅に覆われ、まだまだ記憶も生々しかったです。「震災を『忘れる』」なんて考えられず、「伝える」ことへの関心も(個人的には)さほどありませんでした。むしろ、関東に居て当時のことを色々と質問されるのを煩わしく思っていました。

二番目の記事にある通り、伝えることは簡単ではないですが、「全国から支援があったこと」、「みんなそれぞれの立場で助け合ったこと」、などを伝えないといけないなと思います。とりあえず、ぼくが震災の教訓を聞かれて一番最初に答えるのは「丈夫な家に住んで!」です。←まあ、自明すぎて答えになってるか微妙ですが…(笑)

2012年1月12日木曜日

Neural Prediction Errors Reveal a Risk-Sensitive Reinforcement-Learning Process in the Human Brain


Yael Niv, Jeffrey A. Edlund, Peter Dayan, and John P. O'Doherty
J. Neurosci. 2012;32 551-562
http://www.jneurosci.org/cgi/content/abstract/32/2/551?etoc

試行錯誤で価値を学習する場合でもリスク回避傾向が見られ、その傾向は(非線形な効用関数ではなく)「報酬予測誤差が負の時の学習率を大きくする」ことで実現されている。さらに、これは線条体の活動パターンとも一致する。 http://bit.ly/yTvRLP

Humans and animals are exquisitely, though idiosyncratically, sensitive to risk or variance in the outcomes of their actions. Economic, psychological, and neural aspects of this are well studied when information about risk is provided explicitly. However, we must normally learn about outcomes from experience, through trial and error. Traditional models of such reinforcement learning focus on learning about the mean reward value of cues and ignore higher order moments such as variance. We used fMRI to test whether the neural correlates of human reinforcement learning are sensitive to experienced risk. Our analysis focused on anatomically delineated regions of a priori interest in the nucleus accumbens, where blood oxygenation level-dependent (BOLD) signals have been suggested as correlating with quantities derived from reinforcement learning. We first provide unbiased evidence that the raw BOLD signal in these regions corresponds closely to a reward prediction error. We then derive from this signal the learned values of cues that predict rewards of equal mean but different variance and show that these values are indeed modulated by experienced risk. Moreover, a close neurometric–psychometric coupling exists between the fluctuations of the experience-based evaluations of risky options that we measured neurally and the fluctuations in behavioral risk aversion. This suggests that risk sensitivity is integral to human learning, illuminating economic models of choice, neuroscientific models of affective learning, and the workings of the underlying neural mechanisms.

2012年1月4日水曜日

Anatomical connectivity patterns predict face selectivity in the fusiform gyrus


Zeynep M Saygin, David E Osher, Kami Koldewyn, Gretchen Reynolds, John D E Gabrieli & Rebecca R Saxe
Nature Neuroscience (2011)

A fundamental assumption in neuroscience is that brain structure determines function. Accordingly, functionally distinct regions of cortex should be structurally distinct in their connections to other areas. We tested this hypothesis in relation to face selectivity in the fusiform gyrus. By using only structural connectivity, as measured through diffusion-weighted imaging, we were able to predict functional activation to faces in the fusiform gyrus. These predictions outperformed two control models and a standard group-average benchmark. The structure–function relationship discovered from the initial participants was highly robust in predicting activation in a second group of participants, despite differences in acquisition parameters and stimuli. This approach can thus reliably estimate activation in participants who cannot perform functional imaging tasks and is an alternative to group-activation maps. Additionally, we identified cortical regions whose connectivity was highly influential in predicting face selectivity within the fusiform, suggesting a possible mechanistic architecture underlying face processing in humans.

仕事初め


あけましておめでとうございます。
今年もよろしくお願いします。
(昨日が仕事始めでした。)

去年は(というか一昨年に30歳になってから)何かと体調を崩すことが多かったので、今年は体調管理をしっかりする一年にしたいと思います。