THE HAMSTERS AUDITORY BRAIN-STEM RESPONSE AS A FUNCTION OF STIMULUS-INTENSITY, TONE BURST FREQUENCY, AND HEARING-LOSS

Young adult hamsters were evaluated for normal variations in the auditory brain stem response (ABR) and for the effects of hearing loss. Normal variations in the ABR's latencies and amplitudes were defined for both click and tone burst stimuli over a broad range of intensities. As stimulus intensity decreased from 100 to 15 dB pe SPL, the ABR latencies were prolonged, the P4-P1 interpeak latencies varied in a complex manner, and amplitudes decreased. As tone burst frequency decreased from 8000 to 4000 and then to 2000 Hz, ABR latencies were prolonged, amplitudes decreased, and thresholds increased. The P4-P1 interpeak latencies were also influenced by tone burst frequency, with the longest interpeak latencies occurring in response to the 2000 Hz tons bursts. Data from two hamsters with hearing loss were compared to the normal data to illustrate how the ABR can be used to describe experimentally induced hearing impairment. Hearing impairment was induced by rearing animals in ambient noise. These animals showed elevated ABR thresholds at all three frequencies and upward displacements in the ABR's latency-intensity profiles.