Stability of the Early Components of the Averaged Electroencephalic Response

The early components of the averaged electroencephalic response (AER) were examined at three-hour intervals in eight normal hearing adults over a single, sleepless 24-hour span. During each of the eight sessions, three series of clicks at 50 dB SL were presented to the right ear of the subject as he sat reading. 1024 clicks at the rate of 9.6/sec were used in obtaining each averaged response. Electroencephalic activity was recorded from an electrode on the vertex referred to the left earlobe. The response pattern was very stable, characterized by a polyphasic configuration with mean peak latencies of (P o ) 13.3 msec, (N a ) 22.0 msec, (P a ) 32.3 msec, and (N b ) 45.1 msec. An earlier negative peak (N o ) with a mean peak latency of 8.3 msec occurred in many of the responses. At the conclusion of the 24-hour span, three of the subjects were tested with the same stimuli during various stages of sleep. The early components of the AER remained consistent even during sleep. Threshold searches were successfully carried out on two of the sleeping subjects. The long-term stability of the early components of the AER in the awake and sleep states makes them practical as a response index for electroencephalic audiometry. Their characteristics are more compatible with a neurogenic than with a myogenic theory of their origin.