Effects of social status on prefrontal and hippocampal structure and function in adult female rhesus macaques

This study examined the long-term effects of low social status on adult prefrontal cortex (PFC), hippocampus (HIPPO) structure, functional connectivity and cognitive function using a translational rhesus monkey model.Twenty seven female rhesus monkeys (13 dominant -DOM-, 14 subordinate -SUB-) received structural- and resting-state functional MRI scans to examine the volume of and functional connectivity (FC) between HIPPO and PFC subregions important for executive function, working memory and reward monitoring (dorsolateral PFC(dlPFC) -Area 46-; orbitofrontal cortex(OFC) -Area 13-; medial PFC(mPFC) -Areas 14,25).Our findings show region-specific effects of social status, with bigger HIPPO (F(1,24)=4.824, p=0.038), right OFC (F(1,23)=5.905, p=0.023) and mPFC Area25 in SUB than DOM animals (F(1,24)=4.964, p=0.036). FC between left HIPPO-OFC was also more negatively coupled in SUB than DOM macaques (F(1,10)=3.712, p=0.08). These subjects were also assessed for executive function and cognitive flexibility using an Intra-/Extra-Dimensional (ID/ED) task. Monkeys learned in order: a simple discrimination, three reversal stages, compound stimulus discrimination, intradimensional (ID) shift and extradimensional (ED) shift. Preliminary findings show a positive correlation between OFC volume and Errors during the second reversal (Spearman’s rho=0.727, p=0.011), between the right HIPPO-OFC FC and Errors in the ID-shift (rho=0.810, p=0.015), and a negative correlation between the left HIPPO-mPFC (Area25) FC and Errors in the ID-shift (rho=-0.786, p=0.021).Overall, these findings suggest long-term effects of social status on adult prefrontal and hippocampal structure and connectivity and related cognitive function, suggesting the possibility of long-term neurostructural adaptations in primates with low social status to increase survival in challenging social environments.