P300 in obsessive-compulsive disorder: source localization and the effects of treatment

Converging evidence suggests that frontostriatal abnormalities underlie OCD symptoms. The event-related potential P300 is generated along a widely distributed network involving several of the areas implicated in OCD. P300 abnormalities reported in patients with OCD suggest increased activity in these areas. The aim of the present study was to investigate this assumption in unmedicated patients with OCD, and to assess the effects of OCD treatment on P300 brain activity patterns. Seventy-one unmedicated patients with a DSM-IV diagnosis of OCD and 71 age- and gender-matched healthy control subjects participated in the study. The P300 was obtained through 32-channel EEG during an auditory oddball paradigm. Forty-three patients underwent a second EEG assessment after treatment with sertraline and behavioural therapy. Low-resolution electromagnetic tomography (LORETA) was used to localize the sources of brain electrical activity.

Increased P300-related activity was observed predominantly in the left orbitofrontal cortex, but also in left prefrontal, parietal and temporal areas, in patients compared to controls at baseline. After treatment, reduction of left middle frontal cortex hyperactivity was observed in patients.

Findings of increased activity in frontoparietal areas in patients are consistent with several previous studies. Importantly, OCD treatment led to reduction of hyperactivity in the left middle frontal cortex, an area associated with context processing and uncertainty that might be important for the emergence of OCD symptoms. Thus, the present study is the first to show an association between P300 abnormalities and activity in brain regions postulated to be involved in the pathophysiology of OCD.