 Brain imaging studies demonstrate that the neurophysiological basis of OCD appears to be abnormal functioning of frontal subcortical circuits and that illness symptoms are related to an increase in cortical activity of different areas: anterior cingulate gyrus Saxena Rauch, 2000 orbitofrontal cortex, caudate nucleus, and thalamus. ERP studies provide a number of indicators of cerebral abnormalities in OCD, during critical aspects of cognitive processing Clark et al., 2009. The sharp negative deflection associated with errors is referred to as error-related negativity ERN; Gehring, Coles, Meyer, Donchin, 1995. Gehring et al. 2000 found that OCD patients had an increased ERN amplitude which was significantly associated with symptom severity. Johannes et al. 2001 using a visual discrimination task also reported larger ERN amplitudes in OCD patients, whilst Hajcak and Simons 2002 found increased ERN-like deflections to both incorrect and correct trials in University under- graduates with high levels of obsessive compulsive characteristics. 