It is also possible that the added cognitive demands of the silent-counting oddball task may enhance any P3 asymmetry differences between schizophrenic patients and controls. Although the silent counting task has the advantage of avoiding the problem of motor potentials, it adds an additional working memory load because the subject must keep a running count of the number of oddballs. Neuroimaging studies suggest that maintenance of verbal information in working memory would be expected to increase activation in left frontal, temporal and parietal regions in healthy adults, but not in schizophrenic patients.29,30 In this regard, Salisbury et al.27 reported that their healthy adults had significant left-larger-than-right P3 asymmetry over lateral temporal sites in the silent-counting task, but not in the button-pressing task. Healthy adults tested in tasks with button-presses to oddball tones have actually shown greater P3 amplitude over right than left frontocentral sites,31–33 which is opposite the left-lateralized P3 seen in healthy adults by Salisbury et al.27 for the silent-counting task. Tenke et al.34 found evidence that the right-lateralized P3 in the button-pressing task was related to two different
