Responses of auditory nerve fibers of the unanesthetized decerebrate cat to
click pairs as simulated echoes.
Parham, K. H.B. Zhao and D.O. Kim.
Division of Otolaryngology, Surgical Research Center, Department of
Surgery, Neuroscience Program, The University of Connecticut Health Center,
Farmington, CT 06030-1110, U.S.A..
APStracts 3:0024N, 1996.
SUMMARY AND CONCLUSIONS
1. To elucidate the peripheral contribution to "echo" processing in the
auditory system, we examined the characteristics of auditory nerve responses
to click-pair stimuli in unanesthetized, decerebrate cats. We used equilevel
click pairs at peak levels of 45, 65 and 85 dB SPL re 20 [mu]Pa. The inter-
click intervals ranged from 1 to 32 msec. This study reports results from 78
auditory nerve fibers in 7 cats. The fibers were divided into two groups: 33
low- and 45 high-spontaneous rate (SR), with SRs < and >/= 20 spikes/sec,
respectively. A method was introduced to quantify the second-click response
and its recovery was examined as a function of the inter-click interval. 2. In
general, auditory nerve fibers showed a gradual recovery of the second-click
response as inter-click interval was increased. Noticeable differences in the
second-click response recovery functions emerged among fiber populations which
were related to the SR. Low-SR fibers showed little change in the recovery
functions of the second-click response as the click level was increased from
45 to 85 dB SPL. In contrast, high-SR fibers showed slower recoveries with
increasing click level from 45 to 85 dB SPL. At 45 and 65 dB SPL, the recovery
functions of the two SR groups were similar. At 85 dB SPL, high-SR fibers
exhibited slower recovery than low-SR fibers, regardless of fiber
characteristic frequency. The inter-click intervals at 50% second-click
response ranged from 1 to 6 msec (mean = 1.4 msec) among low-SR fibers. The
inter-click intervals at 50% second-click response for high-SR fibers, while
similar to those for the low-SR fibers at 45 and 65 dB SPL, ranged from 2-16
msec (mean = 3 msec) for high-SR fibers, at 85 dB SPL. 3. We also examined
auditory nerve compound action potentials (CAPs) evoked by click-pair stimuli
for various inter-click intervals and click levels. With increasing inter-
click interval, the amplitude of the second-click CAP increased, and with
increasing level, the second-click CAP showed slower recovery. At 45 dB SPL,
the recovery functions of the second-click CAP were similar to those of the
high- and low-SR fibers. At higher levels, the CAP exhibited lower second-
click response values than both high- and low-SR fiber populations for inter-
click intervals less than 4-8 msec. At 85 dB SPL, as inter-click interval
increased, between 8 and 16 msec, the CAP second-click response converged with
that of the high-SR fibers and by 32 msec, the second-click response values
were similar for the CAP, high- and low-SR fibers. 4. The present results are
consistent with those of forward masking studies at the level of the auditory
nerve in that both demonstrate a short-term reduction of the neural responses.
However, the two results differ in that we observed that high-SR fibers
exhibited slower recovery than low-SR fibers in response to click-pair
stimuli, opposite of the trend observed in the forward masking studies of
responses to pure-tone bursts. 5. The present results on auditory nerve fiber
responses to click-pair stimuli provide a reference for comparison with
responses of central auditory neurons to similar stimuli. This information
should serve to elucidate the peripheral contribution to the processing of
echoes in the auditory system.
Received 29 September 1995; accepted in final form 31 December 1995.
APS Manuscript Number J648-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 29 January 96