numerous prior ERP studies in schizophrenia,1,2 schizophrenic patients showed bilateral reduction in amplitudes of sink and source activity underlying the N2 and P3 components, that is, the defining electrophysiologic correlates of tone discrimination tasks. Notably, patients had marked reductions of N2 sink amplitude over frontocentral sites during the tonal task, and of P3 source amplitude over lateral- and mid-parietal sites during both tasks. It would therefore appear that deficits in stimulus categorization, which are commonly associated with N2, depend on the specific cortical substrate primarily involved in N2 generation – the tonal N2 sink is consistent with possible contributions of anterior cingulate cortex (ACC).95,96 Of critical importance for the present study, however, is that these reductions of N2 sink or P3 source were not greater over the left than right hemisphere. Although the interpretation of the lack of asymmetric P3 reductions is generally problematic, several unique paradigmatic features of the present study strengthen this conclusion.
