Cortical glutamate and GABA are related to compulsive behaviour in individuals with obsessive compulsive disorder and healthy controls

There has been little analysis of neurochemical correlates of compulsive behaviour to illuminate its underlying neural mechanisms. We use 7-Tesla proton magnetic resonance spectroscopy (H-1-MRS) to assess the balance of excitatory and inhibitory neurotransmission by measuring glutamate and GABA levels in anterior cingulate cortex (ACC) and supplementary motor area (SMA) of healthy volunteers and participants with Obsessive-Compulsive Disorder (OCD). Within the SMA, trait and clinical measures of compulsive behaviour are related to glutamate levels, whereas a behavioural index of habitual control correlates with the glutamate:GABA ratio. Participants with OCD also show the latter relationship in the ACC while exhibiting elevated glutamate and lower GABA levels in that region. This study highlights SMA mechanisms of habitual control relevant to compulsive behaviour, 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. The neurochemical basis of compulsive behaviour is not well understood. Here, the authors show that levels of glutamate and GABA in the supplementary motor area and anterior cingulate cortex relate to compulsive behaviour in healthy controls and individuals with OCD.

Automated summary

Little is known about the neurochemical basis of compulsive behavior. This study uses proton magnetic resonance spectroscopy to examine glutamate and GABA levels in the anterior cingulate cortex and supplementary motor area of healthy volunteers and individuals with OCD. The results show that glutamate levels in the supplementary motor area are related to compulsive behavior, while glutamate and GABA levels in the anterior cingulate cortex are associated with habitual control. This study provides insights into the neural mechanisms underlying compulsive behavior.