REDUCTION OF P3(B) IN PATIENTS WITH TEMPORO-PARIETAL LESIONS

By recording event-related EEG potentials from patients with frontal, parietal, or temporo-parietal lesions, we wanted to determine the cort ical area that is relevant to the P3(b) component, replicating the app roach used by Knight and associates [9,11,12,37] who found reduced P3( b)s in patients with temporo-parietal lesions. They used auditory and somatosensory stimuli. We wanted to replicate their findings in audito ry and visual oddball tasks and analysed potentials evoked by targets and by standard stimuli. Temporo-parietal patients' P3(b)s were reduce d with auditory targets and lacked a distinct Pt maximum with visual t argets. Further, auditory N1 was reduced both with targets and standar ds, P3 to visual standards and P2 to auditory standards were reduced. Parietal patients' P3(b)s differed only slightly from the control grou p, being somewhat reduced over the lesioned hemisphere with visual sti muli. Their P3 to visual standards was, however, reduced to the same e xtent as was the temporo-parietal patients'. Frontal patients did not differ from the control group both in their P3(b) and in their P3 to s tandards but had a number of conspicuous features in modality-specific components. In sum, our results on P3(b) (as well as on N1) replicate Knight's findings, confirming his conclusion that integrity of the te mporo-parietal junction is critical for P3(b). Implications for hypoth eses on P3 are discussed.