Middle-latency responses. I. Electrical and acoustic excitation.

The electrically evoked auditory brain-stem response has been used in the past to assess auditory system function with regard to cochlear prosthesis application. The brief latency of the response makes it susceptible to electrical artifact contamination, and waveform identification is often difficult. As a possible alternative for a noninvasive measure of system excitability, the middle-latency response (MLR), elicited by electrical stimulation, was investigated. Middle-latency responses were recorded in response to acoustic and round-window electrical stimulation in albino guinea pigs. Acoustic and electrically evoked MLR waveforms were similar, as were their respective latency/intensity functions. Amplitude/intensity functions for the electric MLR showed greater variability than acoustically evoked MLR functions. The electric MLR is readily evoked and relatively insensitive to electrical artifact in the guinea pig. It is potentially a useful tool in assessing the integrity of auditory pathways and consequently in the development of diagnostic tests for cochlear implant candidates.