Role of Anterior Cingulate Cortex in Self-Reward Representation and Reward Allocation Judgements within Social Context

Published: 9 July 2021| Version 3 | DOI: 10.17632/9f8n5wv6p3.3
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Description

In this study, we aimed to disentangle the neural correlates underlying reward processes and social decision-making since previous findings have been inconsistent. Specifically, we manipulated share sizes of dictator games (DG) and examined the brain activation in response to value of reward for the self/others without or within context using fMRI. Then, we collected data regarding willingness and preference for making these offers in a post-scan behavioral task. Furthermore, we examined how elicited neural activities vary with individual differences from the aspect of self-benefit, altruism, and reward distribution context.

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Three general linear models were created at the first level, and a parametric approach was used. Four event types (first-self, first-other, second-self, and second-other) were used to construct regressors in which event onsets were convolved with the SPM’s canonical hemodynamic response function in each block. These events were modeled with 0.8 s duration for trials where participants answered accurately. Each of these regressors was associated with parametric modulators indicating the amount of money for the agency (Model 1), the likelihood of making the proposal (Model 2), or preference for the proposal (Model 3). The onsets of the questions and responses were also modeled in two regressors across all event types. An additional eleventh regressor may be added to model missing/mistake trials in which the participants did not respond in 4 s or did not answer accurately in some blocks according to participants’ performance. Six head motion parameters modeled the residual effects of head motion as covariates of no interest. Contrast images included the parametric modulator for self and the parametric modulator for the other at the time of the first frame, as well as the second frame. These contrast images were input into a second-level one-sample t-test to examine the regions that parametrically tracked the parametric modulators. The threshold of the statistical maps was at a whole-brain voxel-wise intensity of p < 0.001, with false discovery rate (FDR) correction. The resulting regions of activation were reported in terms of peak voxels in the MNI coordinate space and specified with automated anatomical labeling when mentioned for the first time. For brain regions that overlapped with those in the literature reviewed, alternative names were also provided. We selected the ACC, mPFC, and NAcc as a priori regions of interest (ROIs) based on previous studies that linked responses in these regions to self-reward and other-reward (Apps & Ramnani, 2014; Enzi et al., 2009; Knutson et al., 2005; Lockwood et al., 2015; Lockwood et al., 2018; Moran et al., 2006). We built spheres with a radius of 5 mm centered at the coordinates of the ACCg ([4, 24, 24] Enzi et al., 2009; [8, 32, 12] Lockwood et al., 2015), ACCs ([-3, 19, 38] Moran et al., 2006), mPFC ([-3, 47, 0] Moran et al., 2006), and NAcc ([-11, 11, -4] & [12, 14, -4] Knutson et al., 2005) based on literature evidence using the MarsBaR 0.44 (Brett et al., 2002). Greater neural activity in these regions was correlated with behavioral indices using bivariate correlations. The α value was set at 0.007 using Bonferroni correction (i.e., 0.05/7 ≈ 0.007) to correct for multiple comparisons (7 subscales).