エルゼビア/NSR協賛シンポジウム:社会神経科学「社会的シグナルと意思決定」
NSR-Elsevier sponsored symposium: Social Neuroscience: Social Signal and Decision Making
S3-1-2-1
Neural Mechanisms Underlying Paradoxical Performance for Monetary Incentives Are Driven by Loss Aversion
Neural Mechanisms Underlying Paradoxical Performance for Monetary Incentives Are Driven by Loss Aversion

○下條信輔1
○Shinsuke Shimojo1, Vikram S. Chib1, John P. O’Doherty1
Division of Biology/Computation & Neural Systems, California Institute of Technology1

It is widely assumed that people put more effort and attention to a task as more reward is expected. Thus, performance is commonly expected to be increasing with proposed reward. With this in mind, employers often make payment contingent on performance in order to motivate workers. These assumptions sound reasonable with regard to the ‘ideal decision maker/player” who tries to optimize its strategy to maximize its own gain. However, there are several exceptions in the human performance, including the “choke” phenomenon in which performance is substantially degraded under an enormous pressure due to an extraordinary amount of reward. There have been some psychological speculations on the underlying mechanisms of “choking”, but the exact neural correlates has been unknown.
We used fMRI with a novel incentivized skill task to examine the neural processes underlying behavioral responses to performance-based pay (Chib, et al., Neuron, 2012). We found that individuals’ performance increased with increasing incentives; however, very high incentive levels led to the paradoxical consequence of worse performance, thus successfully duplicating the “choke” phenomenon in the laboratory. From the initial incentive presentation to the task execution, we found that striatal activity rapidly switched between activation and deactivation in response to increasing incentives. To be more specific, the striatal activity was positively correlated with the incentives during the incentive cue presentation (as expected from the literature), but it was surprisingly negatively correlated with it during the motor performance. Critically, decrements in performance and striatal deactivations were directly predicted by an independent measure of behavioral loss aversion. These results suggest that incentives associated with successful task performance are initially encoded as a potential gain; however, when actually performing a task, individuals encode the potential loss that would arise from failure.
Theoretical, as well as the real-world implications will be discussed.
S3-1-2-2
最後通告ゲームでの不公平提案の拒否は何を測っているのか?
What is rejection of unfair offers in the ultimatum game a measure of?

○山岸俊男1
○Toshio Yamagishi1
玉川大学脳科学研究所1
Brain Science Institute, Tamagawa University1

A substantial proportion of people reject unfair offers in the ultimatum game despite the monetary cost that the rejection choice incurs. An ultimatum game is played by two players: proposer and responder. The proposer proposes an offer concerning how to divide a fixed sum of money between him/herself and a responder. The responder decides whether to accept the offer or not. If the responder accepts the offer, both players receive the money according to the proposed division. If the responder rejects the offer, neither the proposer nor the recipient receives reward money at all. By rejecting an offer, the responder looses whatever money he/she could have earned. And yet, it is often the case that more than half of the responders reject offers that give them less than 30% of the total money. Such rejection of unfair offers is usually regarded as costly punishment driven by a social preference of inequity aversion: Players who are unfairly treated by another person seek to restore the unfairness in the outcome by reducing the proposer's money to zero at a cost of reducing their own money to zero as well. This interpretation, however, is inconsistent with the results of experiments by myself and others. First, a substantial proportion of responders reject unfair offers in the impunity game, in which responders lose their money by rejecting the unfair offer while the proposer keeps his/her money intact. By rejecting unfair offers in this game, the responder cannot punish the unfair proposer nor restore equality in the outcome. Furthermore, the rejection choices of unfair offers in the ultimatum game are found not to correlate with fairness-related behaviors in other games such as the prisoner's dilemma game, the trust game, and the dictator game. Responses of the responders to the post-experimental questions suggest that they rejected unfair offers as a means to assert themselves against attempts to subdue them in status competition.
S3-1-2-3
Impulse control in value-based decision-making: Temporal discounting processes
○Jan Peters1
University Medical Center Hamburg-Eppendorf1

Decision-making often involves a trade-off between short-term and long-term outcomes. Typically, humans de-value rewards as the time to their delivery increases, a phenomenon termed temporal discounting. In my talk I will introduce this concept and outline how model-based functional magnetic resonance imaging can help to understand the neural systems supporting these inter-temporal decisions.Impulsive choices of temporally proximal but inferior options are abundant in many disorders of reward and motivation such as substance abuse and pathological gambling. I will focus on excessive reward discounting in gamblers and outline potential neural mechanisms underlying steep reward discounting in gamblers (e.g. elevated striatal-amygdala coupling, altered neural valuation signals in the ventral striatum and ventro-medial prefrontal cortex). I will then show data that suggest that gambling related cues can further increase impulsivity in pathological gamblers via an attenuation of neural valuation signals in the ventral striatum and ventromedial prefrontal cortex. Finally, I will discuss how processes such as subjective time perception and episodic future thinking may modulate inter-temporal choice in healthy subjects and pathological gamblers.
S3-1-2-4
Molecular and neural mechanisms of illusory self-awareness
Molecular and neural mechanisms of illusory self-awareness

○山田真希子1
○Makiko Yamada1
放射線医学総合研究所分子イメージング研究センター1
Molecular Neuroimaging Program, Molecular Imaging Center, National Institute of Radiological Sciences1

The majority of individuals evaluate themselves as superior to average. This is a cognitive bias, called “the superiority illusion”. This illusory self-awareness helps us to have hops for the future, and has been central to the process of human evolution. Possessing this illusion is also important for mental health, as depressed people appear to have a more realistic perception of themselves, called “depressive realism”. Our recent study revealed spontaneous brain functions and central dopamine neurotransmission that generate this illusion, using resting-state fMRI and PET. A functional connectivity between frontal cortex and striatum regulated by inhibitory dopaminergic neurotransmissions determines individual levels of the superiority illusion. This finding suggests that dopamine acts on striatal dopamine receptors to suppress fronto-striatal functional connectivity, leading to disinhibited heuristic approaches to positive self-evaluation. These findings help us to understand how this key aspect of the human mind is biologically determined, and will suggest treatments for depressive realism by targeting specific molecules and neural circuits.
S3-1-2-5
自己概念と実社会における向社会的行動の個人差
Individual difference in self-concept and pro-social behavior in real life

○杉浦元亮1,2
○Motoaki Sugiura1,2
東北大学加齢医学研究所1, 東北大・災害研・人間社会対応2
Insitute of Development, Aging and Cancer, Tohoku University1, Hum Soc. Res. Res. Div., IRIDeS, Tohoku Univ.2

Self-concept, particularly the value of the self in social context, is known to affect pro-social behavior. To investigate the neural mechanism underlying this effect, we examined the relationship between the cortical activation related to self-concept and pro-social behavior in real life. The experiment was performed during the three to four month aftermath of the Tohoku Earthquake in 2011, a serious tsunami disaster. In this period, monetary donation to help tsunami survivors were frequently encouraged in the media. The participants were healthy university students who had experienced short-term difficulties during the earthquake aftermath and were therefore expected to be empathic to the tsunami survivors who were still living a difficult life. The amount of monetary donation was used as an index of pro-social behavior; we expected that the individual difference in self-concept was its dominant modulator, given the relatively homogeneous motivational and socio-economical background of the participants. Using fMRI, we measured the neural activity of 53 participants during a self-personality-trait judgment. Those who donated 100 yen or more and those less than 100 yen were assigned as 'High' and 'Low' donators, respectively. Self-concept-relevant cortical activation and scores of personality-trait questionnaires were compared between two groups. A significant (p<.001, uncorrected) group-difference (High > Low) was identified in the posterior part of the left superior temporal sulcus (pSTS). The score for extroversion in the big five (NEO-FFI) was also higher for the High donators. Considering the implicated role of the pSTS in the inference of another's mental state, the observation was likely to reflect the other-directed self-concept of the High donators; that is, their self-perception and ideal self tend to be affected by the expectation and evaluation of the reference group. This speculation appears consistent with the higher extroversion score in this group.


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