Auditory steady-state responses to click trains from the rat temporal cortex

In order to investigate the mechanisms underlying the generation of steady- state responses (SSRs), auditory evoked potentials elicited by click trains presented at several stimulation rates (30, 40, 50, 60 Hz) were recorded i n 7 awake rats by means of epidural electrodes placed over the temporal cor tex. Mean amplitude-rate function calculated on the recorded responses appe ared almost flat and showed the maximum value at 50 Hz, while mean phases s howed a linear increase when increasing the stimulation rate. In each rat, predictions of the recorded responses at 30, 40, 50 and 60 Hz were synthesi zed by superimposing middle-latency auditory evoked potentials (MAEPs) at s uitable time intervals at each rate. Mean amplitudes calculated on the pred icted curves decreased linearly when increasing the stimulation rate and ap peared higher in comparison to those obtained from the recorded SSRs. Predi cted phases showed a linear increase when increasing the stimulation rate a nd were leading with respect to corresponding phase values calculated for r ecorded SSRs. Our findings indicate that the MAEP superimposition mechanism does not adequately predict the generation of temporal recorded SSRs in ra ts. This was explained by admitting that phenomena related to the recovery cycle and, to a lesser extent, to rate-dependent facilitating effects come into play. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.