In OCD (obsesssive compulsive disorder), there is a hyperconnection between the basal ganglia and the orbitofrontal cortex. So in OCD, there is an abnormality in the cortico-striato-thalamo-cortical (CSTC) circuit, which connects the frontal cortex, striatum, thalamus, and back to cortex. Interestingly, antidepressant medication treatment corrects this abnormality in the CSTC circuit, and thereby reduces OCD symptoms.
In addition, people with OCD have decreased thickness, surface area, and volume of the right anterior cingulate gyrus (ACC). The right lingual gyrus also has decreased surface area in people with OCD.