# Neural Mechanisms of Reciprocity Availability and Expectancy Violation During Social Interaction

## TL;DR

This study explores how the brain responds to social reciprocity and its absence, identifying specific brain regions involved in social bonding and expectation.

## Contribution

The study identifies distinct neural networks associated with reciprocity availability and unavailability during social interactions.

## Key findings

- Reciprocity availability activates ventromedial prefrontal cortex and related regions.
- Reciprocity unavailability increases activity in the left inferior frontal gyrus and temporal pole.
- Personality traits like agreeableness correlate with specific brain activity patterns during reciprocity tasks.

## Abstract

Background: Reciprocity is a core mechanism of social bonding, signaling whether others are available and willing to provide support. The perception of reciprocity availability fosters trust and belonging, whereas its absence may elicit expectancy violation and negative affect. This study investigated the neural correlates of reciprocity availability (RA) and unavailability (RU) during social interaction. Methods: Thirty healthy adults underwent a social task during a functional magnetic resonance imaging (fMRI) scan while viewing short vignettes depicting social exchanges differing in reciprocity cues. Univariate and multivariate (MVPA) analyses were used to identify activation and connectivity patterns associated with RA and RU. Affective responses, reaction times, and personality traits were correlated with neural activity. Results: RA engaged the ventromedial prefrontal cortex, precuneus, temporoparietal junction, and visual cortices. RU elicited greater activation of the left inferior frontal gyrus, dorsomedial prefrontal cortex, and temporal pole, along with enhanced connectivity between visual and parieto-temporal regions. In exploratory analyses, agreeableness correlated with ventromedial prefrontal activation during RA, whereas depressive temperament correlated with temporal pole activity during RU. Conclusions: Reciprocity availability versus unavailability engages distinct large-scale networks for socio-emotional integration and expectancy monitoring, defining a mechanistic framework for studying disrupted reciprocity in psychopathology.