Evidence that the Evoked Response of Dorsomedial Prefrontal Cortex to Fixation Baseline Periods Facilitates Future Social (But not Nonsocial) Inferential (But not non-Inferential) Judgments

Abstract

People draw inferences about each other with great efficiency. Such inferences are typically executed in order to refer transient observed behaviors ( e.g.,“smiling”) to relatively more permanent unobservable states (e.g.,“friendly”). A large body of evidence has delineated a set of brain regions that are reliably correlated with the performance of such mental state inferences: the mentalizing system. Intriguingly, this system shows considerable anatomical overlap with the default mode network, so-called because it is exhibits strong, integrated activity when people are at rest, for instance, duration fixation baseline periods. Here, we used fMRI to test the hypothesis that activity of the mentalizing system during these fixation periods prior to social inferential judgments would increase the efficiency of such judgments. 21 healthy adults underwent event-related fMRI while executing three types of judgments: social inferential (evaluating a mental description of a photographed behavior); social non-inferential (evaluating a motor description of a photographed behavior); or non-social (evaluating an arithmetical expression). Social inferential judgments robustly activated the mentalizing system, and many of the same areas were robustly de-activated by the non-social task when compared to the fixation baseline periods in between each trial. A parametric analysis of response time revealed that increased activity during these pre-trial periods in one of these regions, dorsomedial prefrontal cortex, was associated with faster response times to accurate social (but not non-social) inferential (but not non-inferential) judgments. This provides the best support yet for a functional link between default activity of the mentalizing system and the execution of social inferences.