ENHANCEMENT OF THE AUDITORY-CORTEX EVOKED-RESPONSES IS AWAKE GUINEA-PIGS AFTER NOISE EXPOSURE

In a previous paper [Popelar et al., Hear. Res. 26, 239-247 (1987)] we have shown that amplitudes of the auditory cortex evoked responses (A C-ER) in awake guinea pigs were enhanced for several hours after 1 h o f noise exposure whereas amplitudes of the compound potential of the a uditory nerve (CAP) and of the inferior colliculus evoked responses (I C-ER) declined. The present study demonstrates that the duration of th e AC-ER amplitude increase is related to the intensity of the noise ex posure (white noise, for 30 min or 1 h, intensity range 105-125 dB). T he AC-ER amplitude as well as the threshold shift increased linearly w ith increasing intensity of the noise. The maximum AC-ER increase occu rred when clicks served as stimuli; amplitude enhancement was smaller for 1 kHz tone pips and was absent when 20 kHz tone pips were used. Th e amplitude enhancement was specific for the auditory cortex since the amplitude of visually evoked responses, recorded in the occipital cor tex, was unchanged after noise exposure. It is suggested that the post exposure amplitude enhancement of the AC-ER is produced by temporary e xhaustion of inhibitory processes in the auditory cortex.