Prosocial behavior toward estranged persons modulates the interaction between midline cortical structures and the reward system

学位記番号：医博乙141

メンタルローテーションにおける脳内情報処理機構の研究

University of Tokyo (東京大学

Being in a romantic relationship is associated with reduced gray matter density in striatum and increased subjective happiness

Romantic relationship, a widespread feature of human society, is one of the most influential factors in daily life. Although stimuli related to romantic love or being in a romantic relationship commonly result in enhancement of activation or functional connectivity of the reward system, including the striatum, the structure underlying romantic relationship-related regions remain unclear. Because individual experiences can alter gray matter within the adult human brain, we hypothesized that romantic relationship is associated with structural differences in the striatum related to the positive subjective experience of being in a romantic relationship. Because intimate romantic relationships contribute to perceived subjective happiness, this subjective enhancement of happiness might be accompanied by the experience of positive events related to being in a romantic relationship. To test this hypothesis and elucidate the structure involved, we compared subjective happiness, an indirect measure of the existence of positive experiences caused by being in a romantic relationship, of participants with or without romantic partners (N = 68). Furthermore, we also conducted a voxel-based morphometry (VBM) study of the effects of being in a romantic relationship (N = 113). Being in a romantic relationship was associated with greater subjective happiness and reduced gray matter density within the right dorsal striatum. These results suggest that being in a romantic relationship enhances perceived subjective happiness via positive experiences. Furthermore, the observed reduction in gray matter density in the right dorsal striatum may reflect an increase in saliency of social reward within a romantic relationship. Thus, being in a romantic relationship is associated with positive experiences and a reduction of gray matter density in the right dorsal striatum, representing a modulation of social reward

The neural substrates of the warning effect: a functional magnetic resonance imaging study

To test the hypothesis the warning effect is mediated by the top-down attentional modulation of the motor system, we conducted functional MRI using a Go/No-Go task with visual and auditory warning stimuli. For aurally-warned, visually-prompted trials, the auditory warning stimulus was presented for 1500ms, during which visual cues were presented that prompted either Go or No-Go responses. The same format was used for visually-warned, aurally-prompted trials. Both auditory and visual warning cues shortened the reaction time for the Go trials. The warning cues activated the right-lateralized parieto-frontal top-down attentional network, and motor cortical areas including the pre-supplementary motor area (pre-SMA), the bilateral dorsal premotor cortex, and the left primary motor cortex (M1). The warning-related activation of the pre-SMA matched the difference between its activation by Go-with-warning and by Go-without-warning. Thus, the pre-SMA was primed by the warning cue. The same pre-SMA priming effect was observed for the No-Go cue-related activation, consistent with its role in movement preparation and selection. Similar but less prominent Go cue-related priming was observed in the M1. Thus, the warning effect represents the pre-potentiation of the motor control pathway by the top-down attentional system, from the selection and preparation of the movement to its execution

Medial prefrontal cortex activation is commonly invoked by reputation of self and romantic partners.

The reputation of others influences partner selection in human cooperative behaviors through verbal reputation representation. Although the way in which humans represent the verbal reputations of others is a pivotal issue for social neuroscience, the neural correlates underlying the representation of verbal reputations of others are unclear. Humans primarily depend on self-evaluation when assessing reputation of self. Likewise, humans might primarily depend on self-evaluation of others when representing their reputation. As interaction promotes the formation of more nuanced, individualized impressions of an interaction partner, humans tend to form self-evaluations of persons with whom they are intimate in their daily life. Thus, we hypothesized that the representation of reputation of others is modulated by intimacy due to one's own evaluation formation of that person. To test this hypothesis, we conducted a functional magnetic resonance imaging experiment with 11 pairs of romantic partners while they viewed an evaluation of a target person (self, partner [intimate other], or stranger [non-intimate other]), made by other evaluators. When compared with strangers, viewing evaluations of self and partner activated overlapping regions in the medial prefrontal cortex. Verbal reputation of self-specific activation was found in the precuneus, which represents self-related processing. The data suggest that midline structures represent reputation of self. In addition, intimacy-modulated activation in the medial prefrontal cortex suggests that the verbal reputation of intimate others is represented similarly to reputation of self. These results suggest that the reputation representation in the medial prefrontal cortex is engaged by verbal reputation of self and intimate others stemming from both own and other evaluators' judgments

Neural and Genetic Correlates of the Social Sharing of Happiness

Happiness is regarded as one of the most fundamental human goals. Given recent reports that positive feelings are contagious (e.g., the presence of a happy person enhances others' happiness) because of the human ability to empathize (i.e., sharing emotions), empathic ability may be a key factor in increasing one's own subjective level of happiness. Based on previous studies indicating that a single nucleotide polymorphism in the serotonin 2A receptor gene [HTR2A rs6311 guanine (G) vs. adenine (A)] is associated with sensitivity to emotional stimuli and several mental disorders such as depression, we predicted that the polymorphism might be associated with the effect of sharing happiness. To elucidate the neural and genetic correlates of the effect of sharing happiness, we first performed functional magnetic resonance imaging (fMRI) during a “happy feelings” evocation task (emotional event imagination task), during which we manipulated the valence of the imagined event (positive, neutral, or negative), as well as the presence of a friend experiencing a positive-valence event (presence or absence). We recruited young adult women for this fMRI study because empathic ability may be higher in women than in men. Participants felt happier (p < 0.01) and the mentalizing/theory-of-mind network, which spans the medial prefrontal cortex, temporoparietal junction, temporal poles, and precuneus, was significantly more active (p < 0.05) in the presence condition than in the absence condition regardless of event valence. Moreover, participants with the GG (p < 0.01) and AG (p < 0.05) genotypes of HTR2A experienced happier feelings as well as greater activation of a part of the mentalizing/theory-of-mind network (p < 0.05) during empathy for happiness (neutral/presence condition) than those with the AA genotype. In a follow-up study with a vignette-based questionnaire conducted in a relatively large sample, male and female participants were presented with the same imagined events wherein their valence and the presence of a friend were manipulated. Results showed genetic differences in happiness-related empathy regardless of sex (p < 0.05). Findings suggest that HTR2A polymorphisms are associated with the effect of sharing happiness by modulating the activity of the mentalizing/theory-of-mind network

Raw data for average beta values in the four significant clusters.

<p>Raw data for average beta values in the mPFC (A) and precuneus (B) related to the self reputation, and the two clusters in the mPFC (C) and (D) related to the partner reputation, are shown. Red and white squares show average beta values in the significant clusters of two left-handed subjects and 14 right-handed subjects, respectively.</p

Partner reputation-related activation.

<p>(A) Significant activation related to the reputation effect during the partner condition (partner (reputation>no-reputation)) in comparison with the reputation effect during the stranger condition. Two significant clusters were located in the medial prefrontal cortex (mPFC: [10, 38, 54], [0, 64, 16]). The statistical threshold was set at an uncorrected <i>p</i><0.01 at the voxel level, and at a family-wise error (FWE) corrected <i>p<</i>0.05 at the cluster level. (B) and (C) show the average (SEM) of the beta values in the two clusters located in mPFC.</p