Effects of cortical lesions on middle-latency auditory evoked responses (MLR).

Middle-latency auditory evoked responses (MLRs) were recorded simultaneously at 3 or 4 electrode locations in the coronal plane in 5 normal subjects, 11 patients with temporal lobe lesions and in 5 patients with cortical lesions not involving the temporal lobes. In patients with unilateral temporal lobe lesions, the amplitude of Pa and hence that of the Na-Pa complex was reduced over the involved hemisphere but remained intact over the contralateral hemisphere. No MLR asymmetries were demonstrated in patients with cortical lesions that did not affect the temporal lobes or in 2 cases with unilateral anterior temporal lobectomy. The latency of wave V of the auditory brain-stem response was within normal limits in the majority of the patients studied regardless of the site of their cortical lesion.