BAEP amplitudes and amplitude ratios: relation to click polarity, rate, age and sex

BAEP amplitudes and amplitude ratios in 47 healthy subjects aged 4-58 years have been investigated with respect to the simultaneous influence of stimulus polarity, rate, sex and age. The sex effect (larger amplitudes in women than in men) seemed to be most pronounced for wave IV-V amplitude, while the age effects (decreasing amplitudes with age) seem to be largest for the early waves. The amplitude reductions which followed an increment in the stimulus rate from 10 to 50 Hz were generally larger than the reduction following a change in the stimulus polarity from R to C clicks. The rate-induced amplitude reductions depend on click polarity for waves II and V. Thus, adaptation may be different in C click responding neurons as compared to R click responding neurons. The IV-V/I and IV-V/III amplitude ratios were both independent of sex, but the IV-V/I ratio increased significantly with age. Polarity and rate effects depended on age (wave III) but not on sex. Thus, aging may involve alterations of neural function, while the sex-related amplitude differences may be explained by non-neural factors.