Frequency specificity of brainstem evoked responses in man

Abstract

This report extends previous observations on the acoustical dependencies of human brainstem evoked potentials. We report here on the effect of filtered continuous-noise maskers on the latency and amplitude of click evoked responses. In condition 1, the masker high-frequency cutoff is fixed at 20 kHz, while the low-frequency cutoff varies from 16 to 0 kHz. Progressively extending the low-frequency cutoff produces a decrease in amplitude and an increase in latency of wave V, the most reliably elicited response component. The response is abolished when the low-frequency cutoff is at 2 kHz. In condition 2, the low-frequency cutoff of the masker is fixed at 0 kHz while the high-frequency cutoff is varied from 0.5 to 20 kHz. No latency or amplitude changes appear until the high-frequency cutoff reaches 4 kHz, and the response is abolished at high-frequency settings between 8 and 16 kHz. These experiments demonstrate that click-evoked brainstem responses are generated by high- and middle-frequency fibers, with very little contribution from low-frequency fibers. The latency and amplitude shifts described above do not correlate well with the subjective threshold changes produced by the various maskers, but are better explained on the basis of traveling wave delays at the cochlear level.