fMRI Repetition Suppression During Generalized Social Categorization

Abstract

Correctly identifying friends and foes is integral to successful group living. Here, we use repetition suppression to examine the neural circuitry underlying generalized group categorization-the process of categorizing in-group and out-group members across multiple social categories. Participants assigned to an arbitrary team (i.e., Eagles or Rattlers) underwent fMRI while categorizing political and arbitrary in-group and out-group members. We found that frontoparietal control network exhibited repetition suppression in response to "identical in-group" (Democrat-Democrat or Eagles-Eagles) and "different in-group" (Eagles-Democrat or Democrat-Eagles) trials relative to "out-group/in-group trials" (Republican-Democrat or Rattler-Eagles). Specifically, the repetition suppression contrast map included bilateral superior parietal lobule, bilateral dorsolateral prefrontal cortex (DLPFC), and bilateral middle temporal gyrus. Participants who reported an increased tendency to join and value their social groups exhibited decreased repetition suppression in bilateral DLPFC. Comparison of our whole-brain repetition suppression map with an independently identified map of frontoparietal control network revealed 34.3% overlap. Social categorization requires recognizing both a target's group membership but also the target's orientation toward one's self. Fittingly, we find that generalized social categorization engages a network that acts as a functional bridge between dorsal attentional (exogenously-oriented) and default mode (internally-oriented) networks.

Figure 1

Task Stimuli. Trials consisted of pairs of statements, presented sequentially, in white font against a black background. The experiment included 3 condition types: (a) identical in-groups, (b) different in-groups, or (c) out-group/in-group. Each pair was followed by a 2s prompt that asked them, “How many of the people described were members of your in-group?”

Figure 2

Repetition Suppression. Results from whole-brain contrast of out-group/in-group trials > identical in-group, different in-group trials (red; p < 0.001 corrected from p < 0.005) overlaid on top of resulting FPCN map resulting from (45) (yellow). Orange denotes overlap between the two maps.

Figure 3

Repetition Enhancement. Results from whole-brain contrast of identical in-group, different in-group > out-group/in-group trials (p < 0.001 corrected from p < 0.005).