Actions speak louder than words: Enhanced action tendencies in obsessive-compulsive disorder: An ERP study

Obsessive-compulsive disorder (OCD) is characterized by repeated thoughts and behaviors. Several studies have detected deficient response inhibition ability in individuals with OCD, leading researchers to suggest this deficit as an endophenotype of OCD. However, other researchers maintain that the effect size of this deficit is modest and that it lacks clinical significance. The current investigation examines a potential alternative explanation for difficulties in response inhibition, namely enhanced action tendencies in response to stimuli. Therefore, early processes of motor response preparation preceding action performance (or inhibition) were studied with the event-related potential (ERP) component of readiness potential (RP). RP measures brain reactions related to motor activity in response to external stimuli. ERPs were recorded while 15 participants with OCD and 16 healthy controls performed a variation of a go/no-go task and a stop-signal task using schematic faces (angry and neutral). The OCD group presented with a greater RP slope gradient and amplitude over bilateral parietal areas corresponding to the motor cortex. The amplitude effect was further enhanced under negative valence, compared with the neutral condition. Differences in RP between the OCD and control groups remained significant when controlling for levels of trait anxiety. Results support the hypothesis that a stronger readiness for action might characterize OCD, especially in the presence of threatening stimuli. This finding, specific to OCD and not to anxiety symptoms, may underlie habitual tendencies in OCD. This study suggests that early-stages of motor preparation might be important to the etiology and maintenance of OCD.