Altered cortical excitability in obsessive-compulsive disorder.

Area of Science:

• Neuroscience
• Psychiatry
• Clinical Neurophysiology

Background:

• Obsessive-compulsive disorder (OCD) shares clinical and familial overlap with tic disorders.
• Dysfunction in basal ganglia and linked regions is implicated in both OCD and tic disorders.
• Previous transcranial magnetic stimulation (TMS) studies indicate reduced neuronal inhibition in Tourette's syndrome.

Purpose of the Study:

• To investigate cortical inhibitory and excitatory mechanisms in patients with obsessive-compulsive disorder (OCD).
• To compare cortical excitability in OCD patients with healthy volunteers using TMS.
• To explore the relationship between cortical excitability and comorbid tics in OCD.

Main Methods:

• Applied paired-pulse TMS techniques to 16 OCD patients and 11 healthy volunteers.
• Measured resting motor threshold, active motor threshold, and cortical silent period.
• Assessed intracortical inhibition and facilitation using subthreshold conditioning stimuli.

Main Results:

• OCD patients exhibited significantly decreased intracortical inhibition (ICI) at short interstimulus intervals.
• Increased cortical excitability was indicated by decreased active and resting motor evoked potential thresholds in OCD patients.
• These abnormalities were not medication-related and were more pronounced in OCD patients with comorbid tics.

Conclusions:

• Obsessive-compulsive disorder is associated with abnormal cortical excitability.
• Findings support the hypothesis of analogous disorders with overlapping corticobasal circuit dysfunction between OCD and Tourette's syndrome.
• Tic-related OCD may present with more significant motor cortex excitability alterations than OCD without tics.