ASA 125th Meeting Ottawa 1993 May

5aPP11. Modulation-following responses and peripheral neural adaptation.

Robert L. Smith

Chris Passaglia

My Nguyen

Inst. for Sensory Res., Dept. of Bioeng. and Neurosci., Syracuse Univ., Syracuse, NY 13244-5290

In response to tones that are amplitude modulated by sinusoids, a voltage at the modulation frequency can be recorded from the round window of anesthetized gerbils. This ``modulation following response'' (MFR) displays a number of properties that suggest that it is predominantly composed of summated auditory-nerve responses and may provide a convenient monitor of peripheral neural adaptation. The MFR is a maximum at tone onset and then decays or adapts towards a sustained value that is maintained throughout the duration of the stimulus. At sufficiently low-stimulus intensity levels, the MFR can be reduced by simultaneous or forward masking in a frequency-selective manner similar to the compound action potential (CAP) at tone onset. The MFR is generally eliminated, along with the CAP, by the application of Tetrodotoxin at the round window. The MFR also exhibited a bandpass ``modulation transfer function'' and a complex dependence on intensity level that differ from single-unit response characteristics, and appear to reflect the spatiotemporal summation producing compound responses at the round window. [Work supported by NSF.]