BRAIN-STEM AUDITORY-EVOKED RESPONSES TO CLICKS AND TONE BURSTS IN NOTCHED NOISE IN DALMATIAN PUPPIES

Brain stem auditory-evoked responses (BAERs) were studied in 60 nonane sthetized Dalmatian puppies at 4, 6, and 8 weeks of age. Click stimuli were used in all 60 puppies. Of the puppies with normal click BAERs, responses to 4 kHz, 2 kHz, and 1 kHz tone bursts in notched noise were studied in 24, 5, and 18 puppies, respectively. BAER threshold and wa ve V latency were evaluated in all recordings, and wave I latency was analyzed in BAERs elicited by clicks. The threshold of wave V elicited by clicks did not change significantly over the 4-week period in pupp ies with apparently normal hearing, however, there was a significant d ecrease in the threshold of the BAER to 4 kHz tone bursts in notched n oise. Only three of the 18 8-week-old ''normal-hearing'' puppies had r ecordable responses to 1 kHz tone bursts, All five of the ''normal-hea ring'' puppies presented with 2 kHz tone bursts in notched noise had r eproducible responses; however, an analysis of BAER threshold to this stimulus was not attempted because of the small sample size. The laten cies of both waves I and V in click BAERs decreased significantly over the 4-week period. Similarly, there was a decrease in the latency of wave V elicited by 4 kHz tone bursts in notched noise. Unilateral and bilateral deafness was identified in 13 and 3 of the 60 puppies, respe ctively, as determined by the absence of response to click stimuli at 105 decibels peak sound pressure level (dBpSPL) or greater. Tone burst s of 4 kHz and/or 2 kHz were used in 13 and 8 ears, respectively, of t he 19 ears with sensorineural hearing loss. The use of frequency-speci fic BAERs does not appear to offer any advantage in clinical testing b ut may enhance our understanding of the pattern of normal auditory dev elopment in puppies.