Local effective connectivity changes after transcranial direct current stimulation in obsessive-compulsive disorder patients

This study investigates the effects of transcranial direct current stimulation (tDCS) on brain network connectivity in individuals with obsessive-compulsive disorder (OCD). In a randomized, double-blind, sham-controlled experimental design anodal tDCS (vs. sham) was applied in a total of 43 right-handed patients with OCD, targeting the right pre-supplementary motor area (pre-SMA). Cathodal reference electrode was put on the left pre-SMA. The current was set as 2 mA, with a stimulation duration of either 30 s (sham) or 1200 s. Concurrent resting-state functional MRI data were collected following tDCS (or sham) stimulation. We employed regression dynamic causal modelling (rDCM) to extract whole brain effective connectivity (EC) matrices subsequently analyzing these matrices through graph theory approaches to examine changes in brain activity across different network scales. We found that tDCS compared to sham caused significant changes in local effective connectivity. Increased recruitment level was detectable in the sensorimotor network (SMN), indicating enhanced intra-network connectivity after active tDCS. Clustering coefficient and local efficiency were also found to be increased in the same area. No significant changes were detectable with regard to global network connectivity. Current findings indicate that single-session tDCS can effectively alter local effective connectivities within the SMN in OCD patients. Given the relevance of the SMN and connected regions for the pathophysiology of OCD we believe that tDCS targeting these areas might constitute an effective intervention to normalize altered network connectivity in the disorder of OCD. We used a single tDCS session, which may not reflect long-term effects.