ANATOMICAL SUBSTRATES OF AUDITORY SELECTIVE ATTENTION - BEHAVIORAL AND ELECTROPHYSIOLOGICAL EFFECTS OF POSTERIOR ASSOCIATION CORTEX LESIONS

Event-related brain potentials (ERPs) and reaction times (RTs) were re corded in an auditory selective attention task in control subjects and two groups of patients with lesions centered in (1) the temporal/pari etal junction (T/P, n = 9); and (2) the inferior parietal lobe (IPL, n = 7). High pitched tones were presented to one ear and low pitched to nes to the other in random sequences that included infrequent longer-d uration tones and occasional novel sounds. Subjects attended to a spec ified ear and pressed a button to the longer-duration tones in that ea r. IPL and T/P lesions slowed reaction times (RTs) and increased error rates, but improved one aspect of performance - patients showed less distraction than controls when targets followed novel sounds. T/P lesi ons reduced the amplitude of early sensory ERPs, initially over the da maged hemisphere (N1a, 70-110 ms) and then bilaterally (N1b, 110-130 m s, and N1c 130-160 ms). The reduction was accentuated for tones presen ted contralateral to the lesion, suggesting that N1 generators receive excitatory input primarily from the contralateral ear. IPL lesions re duced N1 amplitudes to both low frequency tones and novel sounds. Nd c omponents associated with attentional selection were diminished over b oth hemispheres in the T/P group and over the lesioned hemisphere in t he IPL group independent of ear of stimulation. Target and novel N2s t ended to be diminished by IPL lesions but were unaffected by T/P lesio ns. The mismatch negativity was unaffected by either T/P or IPL lesion s. The results support different roles of T/P and IPL cortex in audito ry selective attention.