Individual differences in social network size linked to nucleus accumbens and hippocampal volumes in functional neurological disorder: A pilot study

Background: In the biopsychosocial formulation of functional neurological (conversion) disorder (FND), little is known about relationships between social behavior and brain anatomy. We hypothesized that social behavior would relate to brain areas implicated in affiliative behaviors and that social network size would correlate with symptom severity and predisposing vulnerabilities in FND. Methods: This neuroimaging pilot probed how social network size, as measured by the Social Network Index, related to structural brain profiles in 23 patients with motor FND (15 woman and 8 men). FreeSurfer cortical thickness and subcortical volumetric analyses were performed correcting for multiple comparisons. Stratified analyses compared FND patients with a low social network size to matched healthy controls. Secondary exploratory analyses in an expanded sample of 38 FND patients investigated relationships between social network size, risk factors and patient-reported symptom severity. Results: Adjusting for age and gender, neuroimaging analyses showed that social network size positively correlated with left nucleus accumbens and hippocampal volumes in patients with FND; stratified analyses did not show any group-level differences. In individuals with FND, social network size correlated with health-related quality of life, graduating college, working full-time and a non-epileptic seizure diagnosis; social network size inversely related to lifetime trauma burden, post-traumatic stress disorder severity and age. Limitations: Only patient-reported scales were used and social network size information was not collected for healthy subjects. Conclusions: This neuroimaging pilot adds to the literature linking affiliation network brain areas to pro-social behaviors and enhances the biopsychosocial conceptualization of FND.