Effects of aging on middle-latency auditory evoked potentials: a cross-sectional study.

Background: The results of previous studies comparing the middle-latency auditory evoked potentials (MAEPs) of young and elderly subjects have suggested that thalamic inhibitory deficits underlie age-related increases in MAEP amplitudes. Methods: MAEPs were recorded from 73 healthy subjects aged between 20 and 86 years. The latencies of MAEPs recorded at Fz were subjected to two-way analyses of variance for the effects of age group and sex. Amplitude data were subjected to analyses of covariance with age group and sex as between-subjects factors, electrode position as within-subject factor, and individual perceptual thresholds as covariates. Variables exhibiting significant effects of age group were further investigated by regression analysis. Results: Age correlated positively with Na, Na-Pa, and Nb-Pb amplitudes. The distribution of Na-Pa amplitude over the scalp varied with age. Conclusions: The observed age-related increases in amplitude are believed to reflect diminished capacity of subcortical and related cortical systems to inhibit the response to repetitive auditory stimuli that require no attentional effort. Possible age-related changes in the cortical distribution of MAEPs are also discussed.