Structural brain network connectivity in trichotillomania (hair-pulling disorder)

Abstract

Neuroimaging studies suggest involvement of frontal, striatal, limbic and cerebellar regions in trichotillomania, an obsessive-compulsive related disorder. However, findings regarding the underlying neural circuitry remains limited and inconsistent. Graph theoretical analysis offers a way to identify structural brain networks in trichotillomania. T1-weighted MRI scans were acquired in adult females with trichotillomania (n = 23) and healthy controls (n = 16). Graph theoretical analysis was used to investigate structural networks as derived from cortical thickness and volumetric FreeSurfer output. Hubs, brain regions with highest connectivity in the global network, were identified, and group differences were determined. Regions with highest connectivity on a regional level were also determined. There were no differences in small-worldness or other network measures between groups. Hubs in the global network of trichotillomania patients included temporal, parietal, and occipital regions (at 2SD above mean network connectivity), as well as frontal and striatal regions (at 1SD above mean network connectivity). In contrast, in healthy controls hubs at 2SD represented different frontal, parietal and temporal regions, while at 1SD hubs were widespread. The inferior temporal gyrus, involved in object recognition as part of the ventral visual pathway, had significantly higher connectivity on a global and regional level in trichotillomania. The study included women only and sample size was limited. This study adds to the trichotillomania literature on structural brain network connectivity. Our study findings are consistent with previous studies that have implicated somatosensory, sensorimotor and frontal-striatal circuitry in trichotillomania, and partially overlap with structural connectivity findings in obsessive-compulsive disorder.

Keywords: Graph theoretical analysis; Obsessive-compulsive related disorders; Structural network connectivity; Trichotillomania.

Fig. 1

Hub regions at 2 SD within the healthy control [top row] and the TTM group [bottom row]. The hubs in the TTM group were the right (R) supramarginal gyrus (SMG), bilateral inferior temporal gyrus (ITG), left (L) transverse temporal gyrus (TTG) and R cuneus (CUN). The hubs in the control group were the R pars opercularis part of the inferior frontal gyrus (IFG), R posterior cingulate gyrus (PoCG), R superior temporal gyrus (STG) and R entorhinal gyrus (EG). The size of the red circle indicates the number of connections that a hub has in the network. The lobe is indicated at the bottom right by shape- and color-coded legends