title: Neural correlate of human reciprocity in social interactions.
abstract: Reciprocity plays a key role maintaining cooperation in society. However, little is known about the neural process that underpins human reciprocity during social interactions. Our neuroimaging study manipulated partner identity (computer, human) and strategy (random, tit-for-tat) in repeated prisoner's dilemma games and investigated the neural correlate of reciprocal interaction with humans. Reciprocal cooperation with humans but exploitation of computers by defection was associated with activation in the left amygdala. Amygdala activation was also positively and negatively correlated with a preference change for human partners following tit-for-tat and random strategies, respectively. The correlated activation represented the intensity of positive feeling toward reciprocal and negative feeling toward non-reciprocal partners, and so reflected reciprocity in social interaction. Reciprocity in social interaction, however, might plausibly be misinterpreted and so we also examined the neural coding of insight into the reciprocity of partners. Those with and without insight revealed differential brain activation across the reward-related circuitry (i.e., the right middle dorsolateral prefrontal cortex and dorsal caudate) and theory of mind (ToM) regions [i.e., ventromedial prefrontal cortex (VMPFC) and precuneus]. Among differential activations, activation in the precuneus, which accompanied deactivation of the VMPFC, was specific to those without insight into human partners who were engaged in a tit-for-tat strategy. This asymmetric (de)activation might involve specific contributions of ToM regions to the human search for reciprocity. Consequently, the intensity of emotion attached to human reciprocity was represented in the amygdala, whereas insight into the reciprocity of others was reflected in activation across the reward-related and ToM regions. This suggests the critical role of mentalizing, which was not equated with reward expectation during social interactions.
authors.affiliation: Center for Social Research and Data Archives, Institute of Social Science, The University of Tokyo Tokyo, Japan.
authors.forename: Shiro
authors.initials: S
authors.lastname: Sakaiya
authors.affiliation: Department of Politics, Princeton University Princeton, NJ, USA ; Graduate School of Law and Politics, The University of Tokyo Tokyo, Japan.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Shiraito
authors.affiliation: Graduate School of Law and Politics, The University of Tokyo Tokyo, Japan.
authors.forename: Junko
authors.initials: J
authors.lastname: Kato
authors.affiliation: Graduate School of Humanities and Social Sciences, University of Tsukuba Tsukuba, Japan.
authors.forename: Hiroko
authors.initials: H
authors.lastname: Ide
authors.affiliation: Department of Psychology, Senshu University Kawasaki, Japan.
authors.forename: Kensuke
authors.initials: K
authors.lastname: Okada
authors.affiliation: Systems Neuroscience Section, Department of Rehabilitation for Brain Functions, Research Institute of National Rehabilitation Center for Persons with Disabilities Tokorozawa, Japan.
authors.forename: Kouji
authors.initials: K
authors.lastname: Takano
authors.affiliation: Systems Neuroscience Section, Department of Rehabilitation for Brain Functions, Research Institute of National Rehabilitation Center for Persons with Disabilities Tokorozawa, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Kansaku
keywords: DLPFC; VMPFC; amygdala; cooperation; default mode network; reciprocity; reward; theory of mind