Resource scarcity aggravates ingroup bias: neural mechanisms and cross-scenario validation

This study finds out that ingroup bias disappears when survival resources are perceived to be abundant. We exposed the participants and another confederate (ingroup/outgroup member) to a potential threat of unpleasant noise. Each participant received some “relieving resources” to counteract noise administration, the amount of which may or may not be enough for her/him and the confederate in different conditions (i.e., abundance vs. scarcity). First, a behavioral experiment demonstrated that intergroup discrimination manifested only in the scarcity condition; in contrast, the participants allocated similar amounts of resource to ingroup and outgroup members in the abundance condition, indicating a context-dependent allocation strategy. This behavioral pattern was replicated in a follow-up neuroimaging experiment, which further revealed that when contrasting scarcity with abundance, there was higher activation in the anterior cingulate cortex (ACC) as well as stronger functional connectivity of the ACC with the mentalizing network (including the temporoparietal junction and medial prefrontal cortex) for ingroup compared to outgroup members. ACC activation reflects a conflict between self-oriented and other-oriented motives during resource allocation, which is modulated by mentalizing toward ingroup over outgroup in the scarcity condition. Finally, the ACC activation level significantly predicted the influence of resource scarcity on ingroup bias in hypothetical real-life situations according to a follow-up examination.We used a Siemens Prisma 3.0 T MRI machine for data acquisition. Functional volumes were acquired using a multiple slice T2-weighted echo planar imaging (EPI) sequences with the following parameters: repetition time = 1500 ms, echo time = 30 ms, flip angle = 75°, field of view = 192 × 192 mm2, 72 slices covering the entire brain, slice thickness = 2 mm, voxel size = 2 × 2 × 2 mm3.fMRI data were preprocessed in SPM12 (Wellcome Department of Imaging Neurosciences, University College London, U.K., http://www.fil.ion.ucl.ac.uk/spm). Functional data sets underwent slice timing correction, motion correction, were normalized to Montreal Neurological Institute (MNI) space with a spatial resolution of 2 × 2 × 2 mm3, and were smoothed with an isotropic Gaussian kernel of 6 mm and high-pass filtered at a cutoff of 128 s.Behavioral data were processed in IBM SPSS Statistics 20.0.