Auditory-evoked response in the clinically normal dog: Early latency components

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Abstract
SUMMARY: Early latency components (0 to 10 ms) of the auditory-evoked response, which is also called the brainstem auditory-evoked response (baer), were recorded in 6 clinically normal adult dogs. Each dog responded to suprathreshold monaural clicks with a highly repeatable averaged waveform configuration consisting of 6 to 7 vertex positive waves. Configuration of the canine baer consisted mainly of waves I, II, III, V, and VI. Wave IV was present in some records, but in most cases, it formed a complex with wave III and was not apparent as a separate wave. After a 90-dB hearing level (hl) stimulus (20/s), the positive peak of wave I in the averaged response appeared at approximately 1 ms after stimulation onset, and subsequent waves were spaced at approximately ≤ 1-ms intervals. Amplitudes of these waves were 4.0 μV when measured from positive peak to the following negative trough. Experiments were conducted to determine the effects of varying stimulus intensity (50- to 90-dB hl) on baer wave amplitude and peak latency in nonanesthetized and anesthetized dogs and to determine the effects of increasing stimulus rate (10 to 50/s) in nonanesthetized dogs. As stimulus intensity was increased in 10-dB steps from 50 to 90 dB and as the stimulus rate remained at 20/s, amplitude increased and latency decreased for all waves (P < 0.01). When stimulus intensity was held constant at 90 dB and stimulus rate increased from 5 to 50/s, amplitude decreased and latency increased. The amplitude effect was significant for all waves (P ≤ 0.01), whereas the latency effect was only significant for waves III (P ≤ 0.05) and waves V and VI (P ≤ 0.01), Thiamylal sodium (20 mg/kg of body weight, iv) significantly increased the latency of waves II and III (P ≤ 0.05) and waves V and VI (P ≤ 0.01), and decreased the amplitude of waves V and VI (P ≤ 0.01) across intensity levels. The interpeak latency between the positive peaks of waves I and V was calculated from baer in nonanesthetized and anesthetized dogs. Interpeak latency was significantly decreased by decreasing stimulus intensity (P ≤ 0.05) and increased by the administration of thiamylal sodium (P ≤ 0.01). The difference in interpeak latency between right and left sides in nonanesthetized dogs was not affected by stimulus intensity between 50- and 90-dB hl.