2014年4月30日水曜日

The Anterior Cingulate Gyrus Signals the Net Value of Others' Rewards

Matthew A. J. Apps and Narender Ramnani
The Journal of Neuroscience, 30 April 2014, 34(18):6190-6200

ヒト前帯状皮質(ACC)は「他者のNet Value(ベネフィット−コスト)」を保持しているのか?
前帯状溝(ACCs)はコストを保持しており、前帯状回(ACCg)はNet Valueを保持している。

Evaluating the costs and benefits of our own choices is central to most forms of decision-making and its mechanisms in the brain are becoming increasingly well understood. To interact successfully in social environments, it is also essential to monitor the rewards that others receive. Previous studies in nonhuman primates have found neurons in the anterior cingulate cortex (ACC) that signal the net value (benefit minus cost) of rewards that will be received oneself and also neurons that signal when a reward will be received by someone else. However, little is understood about the way in which the human brain engages in cost–benefit analyses during social interactions. Does the ACC signal the net value (the benefits minus the costs) of rewards that others will receive? Here, using fMRI, we examined activity time locked to cues that signaled the anticipated reward magnitude (benefit) to be gained and the level of effort (cost) to be incurred either by a subject themselves or by a social confederate. We investigated whether activity in the ACC covaries with the net value of rewards that someone else will receive when that person is required to exert effort for the reward. We show that, although activation in the sulcus of the ACC signaled the costs on all trials, gyral ACC (ACCg) activity varied parametrically only with the net value of rewards gained by others. These results suggest that the ACCg plays an important role in signaling cost–benefit information by signaling the value of others' rewards during social interactions.

2014年4月17日木曜日

Oxytocin promotes group-serving dishonesty

Shaul Shalvi and Carsten K. W. De Dreu
PNAS vol. 111 no. 15,  5503–5507

オキシトシンを経鼻投与されると、ヒトは「仲間のために」嘘をつくようになる。一方、自分のためにつく嘘の頻度は変わらない。

To protect and promote the well-being of others, humans may bend the truth and behave unethically. Here we link such tendencies to oxytocin, a neuropeptide known to promote affiliation and cooperation with others. Using a simple coin-toss prediction task in which participants could dishonestly report their performance levels to benefit their group’s outcome, we tested the prediction that oxytocin increases group-serving dishonesty. A double-blind, placebo-controlled experiment allowing individuals to lie privately and anonymously to benefit themselves and fellow group members showed that healthy males (n = 60) receiving intranasal oxytocin, rather than placebo, lied more to benefit their group, and did so faster, yet did not necessarily do so because they expected reciprocal dishonesty from fellow group members. Treatment effects emerged when lying had financial consequences and money could be gained; when losses were at stake, individuals in placebo and oxytocin conditions lied to similar degrees. In a control condition (n = 60) in which dishonesty only benefited participants themselves, but not fellow group members, oxytocin did not influence lying. Together, these findings fit a functional perspective on morality revealing dishonesty to be plastic and rooted in evolved neurobiological circuitries, and align with work showing that oxytocin shifts the decision-maker’s focus from self to group interests. These findings highlight the role of bonding and cooperation in shaping dishonesty, providing insight into when and why collaboration turns into corruption.

2014年4月16日水曜日

Neural Mechanisms of Gain–Loss Asymmetry in Temporal Discounting

Saori C. Tanaka, Katsunori Yamada, Hiroyasu Yoneda, and Fumio Ohtake

The Journal of Neuroscience, 16 April 2014, 34(16):5595-5602;

ヒトは将来の報酬を、損失に比べて、多く割り引くことが知られている(サイン効果)。
サイン効果が見られた被験者と見られなかった被験者の脳活動を比較すると、「報酬/損失の遅延時間に対する線条体の活動」及び「報酬/損失額に対する島皮質の活動」に違いがあることが分かった。

Humans typically discount future gains more than losses. This phenomenon is referred to as the “sign effect” in experimental and behavioral economics. Although recent studies have reported associations between the sign effect and important social problems, such as obesity and incurring multiple debts, the biological basis for this phenomenon remains poorly understood. Here, we hypothesized that enhanced loss-related neural processing in magnitude and/or delay representation are causes of the sign effect. We examined participants performing intertemporal choice tasks involving future gains or losses and compared the brain activity of those who exhibited the sign effect and those who did not. When predicting future losses, significant differences were apparent between the two participant groups in terms of striatal activity representing delay length and in insular activity representing sensitivity to magnitude. Furthermore, participants with the sign effect exhibited a greater insular response to the magnitude of loss than to that of gain, and also a greater striatal response to the delay of loss than to that of gain. These findings may provide a new biological perspective for the development of novel treatments and preventive measures for social problems associated with the sign effect.

2014年4月13日日曜日

Activity of striatal neurons reflects social action and own reward

Raymundo Báez-Mendoza, Christopher J. Harris, and Wolfram Schultz
PNAS October 8, 2013 vol. 110 no. 41 16634-16639

「線条体(報酬の処理に関わっている)」のニューロンは社会的報酬の処理にも関わっているのか?

(1)自分の行為の結果、自分に報酬が来る(通常の報酬関連課題)
(2)自分の行為の結果、他者に報酬が行く
(3)他者の行為の結果、自分に報酬が来る
(4)他者の行為の結果、他者に報酬が来る
の四条件を調べた。

線条体のニューロンは、行為者が自分であろうと他者であろうと関係なく、自分の報酬に反応した。
一方、他者の報酬にはほとんど反応しなかった。
また、「行為者(自分 or 他者)」によって反応が変わるニューロンも見つかった。

Social interactions provide agents with the opportunity to earn higher benefits than when acting alone and contribute to evolutionary stable strategies. A basic requirement for engaging in beneficial social interactions is to recognize the actor whose movement results in reward. Despite the recent interest in the neural basis of social interactions, the neurophysiological mechanisms identifying the actor in social reward situations are unknown. A brain structure well suited for exploring this issue is the striatum, which plays a role in movement, reward, and goal-directed behavior. In humans, the striatum is involved in social processes related to reward inequity, donations to charity, and observational learning. We studied the neurophysiology of social action for reward in rhesus monkeys performing a reward-giving task. The behavioral data showed that the animals distinguished between their own and the conspecific’s reward and knew which individual acted. Striatal neurons coded primarily own reward but rarely other's reward. Importantly, the activations occurred preferentially, and in approximately similar fractions, when either the own or the conspecific's action was followed by own reward. Other striatal neurons showed social action coding without reward. Some of the social action coding disappeared when the conspecific's role was simulated by a computer, confirming a social rather than observational relationship. These findings demonstrate a role of striatal neurons in identifying the social actor and own reward in a social setting. These processes may provide basic building blocks underlying the brain's function in social interactions.

2014年4月11日金曜日

Neural activity associated with enhanced facial attractiveness by cosmetics use

Ueno A, Ito A, Kawasaki I, Kawachi Y, Yoshida K, Murakami Y, Sakai S, Iijima T, Matsue Y, Fujii T.
Neurosci Lett. 2014 Mar 2;566C:142-146.

先日お会いした伊藤さん@京大の東北大時代の仕事かな?

同一人物の「化粧をした顔」と「化粧をしていない顔」。
ヒトは前者の方をより魅力的と感じ、それに対応して(報酬系の脳部位である)眼窩前頭皮質の活動も上昇する。

Previous psychological studies have shown that make-up enhances facial attractiveness. Although neuroimaging evidence indicates that the orbitofrontal cortex (OFC) shows greater activity for faces of attractive people than for those of unattractive people, there is no direct evidence that the OFC also shows greater activity for the face of an individual wearing make-up than for the same face without make-up. Using functional magnetic resonance imaging (fMRI), we investigated neural activity while subjects viewed 144 photographs of the same faces with and without make-up (48 with make-up, 48 without make-up, and 48 scrambled photographs) and assigned these faces an attractiveness rating. The behavioral data showed that the faces with make-up were rated as more attractive than those without make-up. The imaging data revealed that the left OFC and the right hippocampus showed greater activity for faces with make-up than for those without make-up. Furthermore, the activities of the right anterior cingulate cortex, left hippocampus, and left OFC increased with increasing facial attractiveness resulting from cosmetics use. These results provide direct evidence of the neural underpinnings of cosmetically enhanced facial attractiveness.

2014年4月10日木曜日

Multiple Neural Mechanisms of Decision Making and Their Competition under Changing Risk Pressure

Nils Kolling, Marco Wittmann, Matthew F.S. Rushworth
Neuron, Volume 81, Issue 5, 1190-1202, 5 March 2014

ハイリスク・ハイリターンな選択肢を選ぶべきか?
自分の置かれている状況によって異なる。
例えば、莫大な借金がある時は、一か八かでハイリスク・ハイリターンな選択肢を選ぶべき。
その調節はヒトでは背側前帯状皮質(dorsal anterior cingulate cortex: dACC)で行われている。

Sometimes when a choice is made, the outcome is not guaranteed and there is only a probability of its occurrence. Each individual’s attitude to probability, sometimes called risk proneness or aversion, has been assumed to be static. Behavioral ecological studies, however, suggest such attitudes are dynamically modulated by the context an organism finds itself in; in some cases, it may be optimal to pursue actions with a low probability of success but which are associated with potentially large gains. We show that human subjects rapidly adapt their use of probability as a function of current resources, goals, and opportunities for further foraging. We demonstrate that dorsal anterior cingulate cortex (dACC) carries signals indexing the pressure to pursue unlikely choices and signals related to the taking of such choices. We show that dACC exerts this control over behavior when it, rather than ventromedial prefrontal cortex, interacts with posterior cingulate cortex.

2014年4月9日水曜日

Integrative Moral Judgment: Dissociating the Roles of the Amygdala and Ventromedial Prefrontal Cortex

Amitai Shenhav and Joshua D. Greene
J. Neurosci. 2014;34 4741-4749

道徳判断の神経基盤。
判断は、扁桃体が「置かれた状況の感情/自動的な側面」を処理し、その情報が前頭前野内腹側部に送られることで行われる。

A decade's research highlights a critical dissociation between automatic and controlled influences on moral judgment, which is subserved by distinct neural structures. Specifically, negative automatic emotional responses to prototypically harmful actions (e.g., pushing someone off of a footbridge) compete with controlled responses favoring the best consequences (e.g., saving five lives instead of one). It is unknown how such competitions are resolved to yield “all things considered” judgments. Here, we examine such integrative moral judgments. Drawing on insights from research on self-interested, value-based decision-making in humans and animals, we test a theory concerning the respective contributions of the amygdala and ventromedial prefrontal cortex (vmPFC) to moral judgment. Participants undergoing fMRI responded to moral dilemmas, separately evaluating options for their utility (Which does the most good?), emotional aversiveness (Which feels worse?), and overall moral acceptability. Behavioral data indicate that emotional aversiveness and utility jointly predict “all things considered” integrative judgments. Amygdala response tracks the emotional aversiveness of harmful utilitarian actions and overall disapproval of such actions. During such integrative moral judgments, the vmPFC is preferentially engaged relative to utilitarian and emotional assessments. Amygdala-vmPFC connectivity varies with the role played by emotional input in the task, being the lowest for pure utilitarian assessments and the highest for pure emotional assessments. These findings, which parallel those of research on self-interested economic decision-making, support the hypothesis that the amygdala provides an affective assessment of the action in question, whereas the vmPFC integrates that signal with a utilitarian assessment of expected outcomes to yield “all things considered” moral judgments.

2014年4月8日火曜日

Cue-Induced Craving Increases Impulsivity via Changes in Striatal Value Signals in Problem Gamblers

Stephan F. Miedl, Christian Buchel, and Jan Peters
J. Neurosci. 2014;34 4750-4755

ギャンブル中毒者は「ギャンブルを連想させる画像」を見ると、時間割引率が高くなる(衝動的になる=直近の報酬を高く評価する)。
また、その際には、中脳と腹側線条体における「価値」の表現方法が(ギャンブルを連想させない画像を見た際とは)異なっている。

Impulsive behavior such as steep temporal discounting is a hallmark of addiction and is associated with relapse. In pathological gamblers, discounting may be further increased by the presence of gambling-related cues in the environment, but the extent to which the gambling relatedness of task settings affects reward responses in gambling addiction is debated. In the present study, human problem gamblers made choices between immediate rewards and individually tailored larger-but-later rewards while visual gambling-related scenes were presented in the background. N = 17 participants were scanned using fMRI, whereas N = 5 additional participants completed a behavioral version of the task. Postscan craving ratings were acquired for each image, and behavioral and neuroimaging data were analyzed separately for high- and low-craving trials (median split analysis). Discounting was steeper for high versus low craving trials. Neuroimaging revealed a positive correlation with model-based subjective value in midbrain and striatum in low-craving trials that was reversed in high-craving trials. These findings reveal a modulation of striatal reward responses in gamblers by addiction-related cues, and highlight a potentially important mechanism that may contribute to relapse. Cue-induced changes in striatal delayed reward signals may lead to increased discounting of future rewards, which might in turn affect the likelihood of relapse.

2014年4月3日木曜日

Attributing awareness to oneself and to others

Yin T. Kelly, Taylor W. Webb, Jeffrey D. Meier, Michael J. Arcaro, and Michael S. A. Graziano
Proceedings of the National Academy of Sciences 1 April 2014; Vol. 111, No. 13

「他者がある物体を(視覚的に)認識しているか?」を判断する際にはTPJ(側頭頭頂接合部)が活動する。
一方、TMSを用いてTPJの活動を人為的に抑制すると、(被験者自身の)物体の認識がうまくできなくなる。
→「他者の物体認識についての判断」と「自分自身の(視覚的)物体認識」は同じ脳領域で行われている。

This study tested the possible relationship between reported visual awareness (“I see a visual stimulus in front of me”) and the social attribution of awareness to someone else (“That person is aware of an object next to him”). Subjects were tested in two steps. First, in an fMRI experiment, subjects were asked to attribute states of awareness to a cartoon face. Activity associated with this task was found bilaterally within the temporoparietal junction (TPJ) among other areas. Second, the TPJ was transiently disrupted using single-pulse transcranial magnetic stimulation (TMS). When the TMS was targeted to the same cortical sites that had become active during the social attribution task, the subjects showed symptoms of visual neglect in that their detection of visual stimuli was significantly affected. In control trials, when TMS was targeted to nearby cortical sites that had not become active during the social attribution task, no significant effect on visual detection was found. These results suggest that there may be at least some partial overlap in brain mechanisms that participate in the social attribution of sensory awareness to other people and in attributing sensory awareness to oneself.

2014年4月2日水曜日

Disentangling neural representations of value and salience in the human brain

Thorsten Kahnt, Soyoung Q Park, John-Dylan Haynes, and Philippe N. Tobler
Proceedings of the National Academy of Sciences 1 April 2014; Vol. 111, No. 13

脳内での「価値(value)」と「顕著性(salience)」の処理。後部頭頂皮質の中で、上部が価値、下部が顕著性をコードしている。また、眼窩前頭皮質は価値をコードしている. http://www.pnas.org/content/111/13/5000

A large body of evidence has implicated the posterior parietal and orbitofrontal cortex in the processing of value. However, value correlates perfectly with salience when appetitive stimuli are investigated in isolation. Accordingly, considerable uncertainty has remained about the precise nature of the previously identified signals. In particular, recent evidence suggests that neurons in the primate parietal cortex signal salience instead of value. To investigate neural signatures of value and salience, here we apply multivariate (pattern-based) analyses to human functional MRI data acquired during a noninstrumental outcome-prediction task involving appetitive and aversive outcomes. Reaction time data indicated additive and independent effects of value and salience. Critically, we show that multivoxel ensemble activity in the posterior parietal cortex encodes predicted value and salience in superior and inferior compartments, respectively. These findings reinforce the earlier reports of parietal value signals and reconcile them with the recent salience report. Moreover, we find that multivoxel patterns in the orbitofrontal cortex correlate with value. Importantly, the patterns coding for the predicted value of appetitive and aversive outcomes are similar, indicating a common neural scale for appetite and aversive values in the orbitofrontal cortex. Thus orbitofrontal activity patterns satisfy a basic requirement for a neural value signal.

2014年4月1日火曜日

A neural mechanism underlying failure of optimal choice with multiple alternatives

Bolton K H Chau, Nils Kolling, Laurence T Hunt, Mark E Walton & Matthew F S Rushworth
Nature Neuroscience (2014) doi:10.1038/nn.3649

二つの選択肢間の意思決定において,三番目の選択肢が現れたらどうなるのか?
「三番目の選択肢の価値が低い」時の方が,元々の選択が正確にできなくなる.
また,その際には,「二つの選択肢の価値の差」をコードしている前頭前野内腹側部(vmPFC)の活動が低下している.

Despite widespread interest in neural mechanisms of decision-making, most investigations focus on decisions between just two options. Here we adapt a biophysically plausible model of decision-making to predict how a key decision variable, the value difference signal—encoding how much better one choice is than another—changes with the value of a third, but unavailable, alternative. The model predicts a surprising failure of optimal decision-making: greater difficulty choosing between two options in the presence of a third very poor, as opposed to very good, alternative. Both investigation of human decision-making and functional magnetic resonance imaging–based measurements of value difference signals in ventromedial prefrontal cortex (vmPFC) bore out this prediction. The vmPFC signal decreased in the presence of low-value third alternatives, and vmPFC effect sizes predicted individual variation in suboptimal decision-making in the presence of multiple alternatives. The effect contrasts with that of divisive normalization in parietal cortex.