The brain stem response SN10, its frequency selectivity, and its value in classifying neural hearing lesions.

The component P6 of the brain stem is only to be related to the hearing ability in the high tone range of greater than or equal to 2 kHZ, but it can be traced up to the hearing threshold. The cortex response N90, on the other hand, is frequency-specific, but it can hardly be recorded up to the subjective hearing threshold. The slow brain stem response SN10 (Davis and Hirsh 1979), unaffected by medicamented sleep, shall give information about hearing ability in the low and medium frequency range and may thus be an ideal complement to the fast response P6. In a number of normal hearing people and patients with sensorial hearing impairment of different frequency characteristics the brain stem responses P6 and SN10 were simultaneously recorded. As stimuli we used tone pips of a rise and fall time independent of frequency of about 2 ms and with a plateau of 2 ms as well. The mean threshold of the SN10 response is about 10 dB above the subjective hearing threshold. The constancy of the latencies corresponds to that of P6. The frequency selectivity of this relatively slow brain stem response is proved by comparing the P6 and SN10 responses with the course of the subjective hearing threshold. The topodiagnostic significance of the wave SN10 in connection with the brain stem response P6 and the cortical response N90 is shown in a case of neural hearing impairment.