of both left and right temporal lobes.1,22 Further complicating the interpretation of these conflicting findings is evidence showing that reduced P3 may be associated with reversed asymmetries in schizophrenia when handedness is considered, with right-handed patients showing greater reductions of the left temporal regions, and left-handed patients show the opposite pattern.23 In a meta-analysis of P300 asymmetry in schizophrenia, Jeon and Polich24 found no consistent asymmetrical P3 reductions; however, effect sizes for group comparisons were nevertheless larger over left than right temporal sites. Although clinical or neuroanatomical differences between patients may account for the difference in P3 findings across these studies, another important contributor could be the different response modes used in the oddball tasks.13 Most studies in which ERPs were recorded during silent counting of oddball tones found greater reduction of P3 amplitude over left (T7) than right (T8) temporal lobe sites in schizophrenic patients (cf. Pivik et al.25 for modifications to the 10–20 system electrode nomenclature), whereas only a few studies using a button press response found this P3 asymmetry.
