XI Cerebral Evoked Response to Auditory Stimuli in Waking Man

Abstract

Evoked response from the waking human brain to auditory stimuli was studied with the aid of an average response computer of the analog type. The subjects were 19 adults, 10 older children ranging in age from 11 to 15 years and 12 younger children aged 6 to 10 years. Pure tone of 500, 1,000, 2,000 and 4,000 cps were used as the stimuli. As a rule, 50 single runs were averaged by the computer. With the adult subjects, the response was detected in 25, 70 and 100% of the total observations when the stimulus intensities were at 0, 10 and 20 db [decibels] above their subjective thresholds respectively. On the other hand, with the younger children, the response was recognized in only 58% of the subjects at 20 db above their subjective thresholds, but more than 90% of the subjects showed the response when the stimulus intensity was 40 db above threshold. The typical waveform of the V potential was triphasic the most prominent negative deflection (N1) was followed by a positive (P2) and a slow negative deflection (N2). Their mean peak latencies in the adult subjects were 123, 199 and 291 msec respectively with the stimulus intensity at 20 db. A slight prolongation in the peak latencies was found in the young children at the intensity level of 20 db. The mean amplitude from N1 to P2 was 10.8 microvolts per single stimulus at 20 db in the adult subjects, whereas it averaged only 6.9 microvolts in the young children. The amplitude of the response was a linear function of the stimulus intensity in decibel values. A comparative study showed that the responses was detectable more easily by the averaging technique than by the superimposition method of Dawson.