Growth of evoked potential amplitude in neonatal chicks exposed to intense sound.

The recovery of auditory function at selected intervals following exposure to a 0.9 kHz tone for 48 h at 120 dB SPL is described in neonatal chicks. Evoked potentials recorded from the nucleus magnocellularis were used to measure threshold sensitivity and peak-to-peak response amplitude as a function of stimulus intensity. The relation between evoked-response amplitude and stimulus intensity was nearly linear in control animals. However, at 10 days post exposure, the evoked response in mid-range frequencies showed a severe threshold shift and an abnormally rapid growth in amplitude. At 3 days post exposure, the rate of growth was nearly identical to that measured in control animals and threshold sensitivity showed considerable recovery. Current theories of amplitude-intensity growth and studies of basilar papilla damage and repair following intense sound exposure were applied in the analysis of these results.