The effect of sleep on the auditory brainstem response (ABR) and the middle latency response (MLR)

The ABR and the MLR were measured without interruption in 4 subjects during a whole night of natural sleep and compared with the awake responses. The conventional EEG activity was monitored during the whole procedure, which permitted a precise rating of the sleep stage during each recording period. Only minor changes were found in the latencies for the ABR during sleep. The MLR responses showed quite dramatic changes in morphology and latencies. Our results appear to indicate that the 40/sec stimulus presentation mode of the MLR will not be very effective during sleep due to the pronounced latency shifts of the different peaks in the MLR. The 40/sec response is based on an inter-peak latency of 25 msec. If this presumption is not fulfilled the different waves in the 40/sec response will not be superimposed and consequently enhanced in the averaging procedure.