The default mode network in chimpanzees (Pan troglodytes) is similar to that of humans

Abstract

The human default mode network (DMN), comprising medial prefrontal cortex, precuneus, posterior cingulate cortex, lateral parietal cortex, and medial temporal cortex, is highly metabolically active at rest but deactivates during most focused cognitive tasks. The DMN and social cognitive networks overlap significantly in humans. We previously demonstrated that chimpanzees (Pan troglodytes) show highest resting metabolic brain activity in the cortical midline areas of the human DMN. Human DMN is defined by task-induced deactivations, not absolute resting metabolic levels; ergo, resting activity is insufficient to define a DMN in chimpanzees. Here, we assessed the chimpanzee DMN's deactivations relative to rest during cognitive tasks and the effect of social content on these areas' activity. Chimpanzees performed a match-to-sample task with conspecific behavioral stimuli of varying sociality. Using [(18)F]-FDG PET, brain activity during these tasks was compared with activity during a nonsocial task and at rest. Cortical midline areas in chimpanzees deactivated in these tasks relative to rest, suggesting a chimpanzee DMN anatomically and functionally similar to humans. Furthermore, when chimpanzees make social discriminations, these same areas (particularly precuneus) are highly active relative to nonsocial tasks, suggesting that, as in humans, the chimpanzee DMN may play a role in social cognition.

Keywords: comparative cognition; functional neuroimaging; social cognition.

Figure 1.

Imaging contrasts. t-Statistic maps are thresholded at P < 0.05, uncorrected for multiple comparisons. Color bar indicates value of t-statistic. For clarity of presentation, all t-statistics >6 are presented as red. Anterior medial prefrontal cortex (MPFC), precuneus (PCun), and posterior cingulate cortex (PCC) are labeled. The cerebellum and brainstem have been masked out of these analyses. (A) rest–social task #1 (3 mm right of midline). (B) rest–nonsocial task (3 mm right of midline). (C) social task #1–nonsocial task (midline). (D) social task #2–nonsocial (midline). (E) low social task–nonsocial task (midline). (F) All social tasks–nonsocial task (midline).

Figure 2.

ROI centered around highest area of activation in precuneus.

Figure 3.

Levels of normalized metabolic activity in the precuneus ROI in each condition. Within subject repeated-measures ANOVA, P < 0.009.