Inhibition-related differences between tic-free and tic-related obsessive-compulsive disorder: evidence from the N2 and P3.

Tic-related OCD (obsessive-compulsive disorder) was introduced as an OCD subtype in the DSM-5 based mainly on family and clinical data that showed differences between OCD in dependence of accompanying tics. Little is known, however, regarding neurocognitive differences between subtypes. We used the stop-signal task to examine whether differences exist in response inhibition between OCD patients without tics (n = 21), patients with tic-related OCD (n = 12), and 21 healthy controls. The groups were carefully matched for gender, age and level of education. The stop-signal reaction time (SSRT) and inhibition-related N2 and P3 were used to examine behavioral and neural correlates of response inhibition and inhibition-related processes. In the SSRT, no difference was found between groups. P3 amplitude was larger in tic-free compared to tic-related OCD and healthy controls. No group differences were found in the N2 amplitude. For tic-related OCD, SSRT data indicate intact response inhibition, and P3 data indicate intact neural aftereffects of inhibition like the evaluation of the outcome. This is similar to what is found in patients with TD and may, thus, be interpreted as a support for shared mechanisms in relation to TD. In OCD, alterations in P3 amplitude indicate hyperactivity in the evaluation of the outcome of the inhibition process. This is in line with hyperactivity generally found in performance monitoring in OCD.