Journal of Neurophysiology, Vol 60, Issue 2 569-579, Copyright © 1988 by APS

ARTICLES

Effect of electrical stimulation of the crossed olivocochlear bundle on temporary threshold shifts in auditory sensitivity. II. Dependence on the level of temporary threshold shifts

R. Rajan
Department of Physiology, University of Western Australia, Nedlands.

1. This report presents a more detailed examination of crossed olivocochlear bundle (COCB) effects on temporary threshold shifts (TTS). The principal aim was to establish the details of the relationship between the effects of continuous COCB stimulation and the TTS caused by various exposures. Initially, in various groups, different intensities of a 1-min exposure were presented with or without COCB stimulation. Stimulation at any particular rate caused greatest reductions in TTS to occur for the higher intensity exposures than for the lower intensity ones. Thus COCB stimulation at 140 pulses/s reduced maximum threshold losses by the following amounts: 13.33 [106 dB sound pressure level (SPL) exposure], 13.29 (103 dB SPL exposure), 8.9 (101 dB SPL exposure), and 0.77 dB (97 dB SPL exposure). 2. The effect of COCB stimulation was also examined on a shorter duration (30 s) exposure causing TTS intermediate between that due to 1-min exposure at 97 dB SPL and that at 101 dB SPL. Reductions in TTS to the shorter duration exposure were not obtained with COCB stimulation at 140 pulses/s but only when the rate was increased to 260/s. 3. Thus COCB stimulation at any particular rate caused greatest reductions in TTS when the exposure would have caused a large amount of TTS, regardless of the intensity or duration of exposure. These two parameters of the exposure could be traded to provide a level of TTS that would be affected by a standard COCB stimulus. Low-level exposures that caused only small amounts of TTS were not affected by the standard COCB stimulus. As the level of the exposure, and therefore, the ensuing TTS, increased (with increased duration or intensity of exposure), the standard stimulus had greater effects. Increasing the rate of pulses in the COCB stimulus resulted in the low-level exposures now being affected. Even at the higher rate, greatest reductions in TTS were obtained when the exposure would have resulted in high levels of TTS. 4. In an attempt to determine the site of action of the continuous COCB stimulus the endocochlear potential (EP) and the summating potential (SP) were recorded from scala media of the basal turn while applying COCB stimuli similar to those used in the TTS experiments. Although the continuous COCB stimulus caused the traditional changes in the EP and SP associated with COCB stimulation with pulsed short electrical trains, these changes adapted quite rapidly and did not persist for the amount of time shown to be necessary for full reductions in TTS to be obtained.(ABSTRACT TRUNCATED AT 400 WORDS)

This article has been cited by other articles:

				S. F. Maison, T. W. Rosahl, G. E. Homanics, and M. C. Liberman Functional Role of GABAergic Innervation of the Cochlea: Phenotypic Analysis of Mice Lacking GABAA Receptor Subunits {alpha}1, {alpha}2, {alpha}5, {alpha}6, beta2, beta3, or {delta} J. Neurosci., October 4, 2006; 26(40): 10315 - 10326. [Abstract] [Full Text] [PDF]

				R. Rajan Contextual Modulation of Olivocochlear Pathway Effects on Loud Sound-Induced Cochlear Hearing Desensitization J Neurophysiol, April 1, 2005; 93(4): 1977 - 1988. [Abstract] [Full Text] [PDF]

				R. Rajan Unilateral Hearing Losses Alter Loud Sound-Induced Temporary Threshold Shifts and Efferent Effects in the Normal-Hearing Ear J Neurophysiol, March 1, 2001; 85(3): 1257 - 1269. [Abstract] [Full Text] [PDF]

				S. G. Kujawa and M. C. Liberman Long-Term Sound Conditioning Enhances Cochlear Sensitivity J Neurophysiol, August 1, 1999; 82(2): 863 - 873. [Abstract] [Full Text] [PDF]

				E. J. Walsh, J. McGee, S. L. McFadden, and M. C. Liberman Long-Term Effects of Sectioning the Olivocochlear Bundle in Neonatal Cats J. Neurosci., May 15, 1998; 18(10): 3859 - 3869. [Abstract] [Full Text] [PDF]

				S. G. Kujawa and M. C. Liberman Conditioning-Related Protection From Acoustic Injury: Effects of Chronic Deefferentation and Sham Surgery J Neurophysiol, December 1, 1997; 78(6): 3095 - 3106. [Abstract] [Full Text] [PDF]

				S. Maison, C. Micheyl, and L. Collet Medial Olivocochlear Efferent System in Humans Studied With Amplitude-Modulated Tones J Neurophysiol, April 1, 1997; 77(4): 1759 - 1768. [Abstract] [Full Text] [PDF]