Neurobehavioral and neurochemical basis of compulsive behavior: A 7T magnetic resonance spectroscopy study in humans

Abstract

There has been relatively little analysis of possible neurochemical correlates of compulsive behavior to illuminate its underlying neural mechanisms. We utilised 7-Tesla proton magnetic resonance spectroscopy (1H-MRS) to assess the balance of excitatory and inhibitory neurotransmission by measuring glutamate and GABA levels in anterior cingulate cortex and supplementary motor area (SMA) of healthy volunteers and patients with Obsessive-Compulsive Disorder (OCD). Within the SMA, trait and clinical measures of compulsive behavior were related to glutamate levels, whereas a behavioral index of habitual control correlated with the glutamate:GABA ratio. OCD patients additionally exhibited elevated glutamate levels and glutamate:GABA ratios in anterior cingulate cortex which also correlated with habitual control. This study highlights important underlying relationships between SMA mechanisms of habitual control relevant to compulsive behavior, common to the healthy sub-clinical and OCD populations. The results also demonstrate additional involvement of anterior cingulate in the balance between goal-directed and habitual responding in OCD.