What can clinical disorders involving the basal ganglia tell us about the pathophysiology of obsessive and compulsive symptoms?

The neurobiology and pathological mechanisms underlying obsessive-compulsive symptoms have been explored in the literature for more than fifty years without reaching a definitive conclusion. What is clear is that some brain areas, including the basal ganglia and connected structures, have been implicated through several different approaches, including use of animal models and examination of human subjects with different cerebral lesions and pathologies. The purpose of this narrative review is to explore how examination of disorders affecting the basal ganglia can give insights into the pathophysiology of obsessive-compulsive symptoms and obsessive-compulsive disorder. These clinical conditions include Parkinson's disease, Huntington's disease, paediatric autoimmune neuropsychiatric disorders associated with streptococcal infections (PANDAS), Sydenham's chorea, and Tourette's syndrome. We review neuroimaging, genetic, and clinical studies in these conditions. Overall, the literature discussed supports the idea that the reward circuitry, including the limbic and lateral orbitofrontal loops of the basal ganglia, as well as goal-directed versus habitual pathways in the dorsal striatum, are involved in obsessive-compulsive disorder and obsessive-compulsive symptoms.