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 cortical area that is relevant to the P3_b component, replicating the approach used by Knight and associates [9,11,12,37] who found reduced P3_bs in patients with temporo-parietal lesions. They used auditory and somatosensory stimuli. We wanted to replicate their findings in auditory and visual oddball tasks and analysed potentials evoked by targets and by standard stimuli. Temporo-parietal patients' P3_bs were reduced with auditory targets and lacked a distinct Pz maximum with visual targets. Further, auditory N1 was reduced both with targets and standards, P3 to visual standards and P2 to auditory standards were reduced. Parietal patients' P3_bs differed only slightly from the control group, being somewhat reduced over the lesioned hemisphere with visual stimuli. Their P3 to visual standards was, however, reduced to the same extent 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 standards 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 temporo-parietal junction is critical for P3_b. Implications for hypotheses on P3 are discussed.