INTENSITY DEPENDENCE OF AUDITORY-EVOKED POTENTIALS IN BEHAVING CATS

The intensity dependence of auditory evoked potentials (AEPs) recorded epidurally over the primary (AI) and secondary (AII) areas of the aud itory cortex was studied in behaving cats during wakefulness, sleep an d anesthesia. Four kHz tones of 50, 60, 70, and 80 dB SPL, presented i n random order every 2 +/- 0.2 s by a bone conductor, elicited clear c hanges of the AEP amplitudes with increasing stimulus intensity, but i ndividual components displayed different response curves. AEP componen ts from the AI region showed saturation of their amplitude with stimul us intensify (P13, P34) or no amplitude increase (N19), while amplitud e and intensity were linearly related in the An area. The intensity de pendence of the first positive component (P12/P13) was consistently st ronger for the AEP recorded from the AI than from the AII area: while later components exhibited no difference between AI and AII. During sl ow wave sleep, the intensity dependence of this first positive compone nt increased in the two areas, while that of later components decrease d. Pentobarbital anesthesia abolished almost all later components and depressed the intensity dependence of the first positive component bot h in the AI and AII area. These results indicate that (1) clear intens ity dependence of AEP exists in the cat auditory cortex and (2) this i ntensity dependence, especially that of the first positive AEP compone nt, shares functional similarities to the human augmenting/reducing ph enomenon in the auditory modality concerning regional differences and sleep-waking cycle.