Journal of Neurophysiology, Vol 73, Issue 2 449-467, Copyright © 1995 by APS

ARTICLES

Temporal resolution of neurons in cat inferior colliculus to intracochlear electrical stimulation: effects of neonatal deafening and chronic stimulation

R. Snyder, P. Leake, S. Rebscher and R. Beitel
Epstein Laboratory, University of California, San Francisco 94143-0526, USA.

1. Cochlear implants have been available for > 20 yr to profoundly deaf adults who have lost their hearing after acquiring language. The success of these cochlear prostheses has encouraged the application of implants in prelingually deaf children as young as 2 yr old. To further characterize the consequences of chronic intracochlear electrical stimulation (ICES) on the developing auditory system, the temporal-response properties of single neurons in the inferior colliculus (IC) were recorded in deafened anesthetized cats. 2. The neurons were excited by unilateral ICES with the use of a scala tympani stimulating electrode implanted in the left cochlea. The electrodes were modeled after those used in cochlear implant patients. Responses of 443 units were recorded extracellularly in the contralateral (right) IC with the use of tungsten microelectrodes. Recordings were made in three groups of adult animals: neonatally deafened/chronically stimulated animals (192 units), neonatally deafened/unstimulated animals (80 units), and adult-deafened/prior normal-hearing animals (171 units). The neonatally deafened cats were deafened by multiple intramuscular injections of neomycin sulfate and never developed demonstrable hearing. Most of the deafened, chronically stimulated animals were implanted at 6 wk of age and stimulated at suprathreshold levels for 4 h/day for 3-6 mo. The unstimulated animals were implanted as adults at least 2 wk before the acute physiological experiment and were left unstimulated until the acute experiment was conducted. Prior-normal adults were deafened and implanted at least 2 wk before the acute experiment. 3. IC units were isolated with the use of a search stimulus consisting of three cycles of a 100-Hz sinusoid. Most units responded to sinusoidal stimulation with either an onset response or a sustained response. Onset units were the predominant unit found in the external nucleus, whereas sustained units were found almost exclusively in the central nucleus. The temporal resolution of sustained response units was measured with the use of pulse trains of increasing frequency and calculating the discharges/pulse. 4. The range of electrical pulse frequencies to which IC units responded in a temporally synchronized manner was comparable with that produced by acoustic stimulation. The discharge rate/pulse-versus-pulse frequency transfer functions of IC units were uniformly low-pass, although they varied widely in their cutoff frequencies. This variation in pulse response was partially correlated with the unit's response to sinusoids. Most onset neurons responded only to pulse frequencies below 20 pulses per second (pps). Most sustained units responded best to pulse frequencies < 100 pps, and most ceased to respond to pulse frequencies > 300 pps.(ABSTRACT TRUNCATED AT 400 WORDS)

This article has been cited by other articles:

				Z. M. Smith and B. Delgutte Sensitivity of Inferior Colliculus Neurons to Interaural Time Differences in the Envelope Versus the Fine Structure With Bilateral Cochlear Implants J Neurophysiol, May 1, 2008; 99(5): 2390 - 2407. [Abstract] [Full Text] [PDF]

				M. Vollmer, R. E. Beitel, R. L. Snyder, and P. A. Leake Spatial Selectivity to Intracochlear Electrical Stimulation in the Inferior Colliculus is Degraded After Long-Term Deafness in Cats J Neurophysiol, November 1, 2007; 98(5): 2588 - 2603. [Abstract] [Full Text] [PDF]

				Z. M. Smith and B. Delgutte Sensitivity to Interaural Time Differences in the Inferior Colliculus with Bilateral Cochlear Implants J. Neurosci., June 20, 2007; 27(25): 6740 - 6750. [Abstract] [Full Text] [PDF]

				M. Vollmer, P. A. Leake, R. E. Beitel, S. J. Rebscher, and R. L. Snyder Degradation of Temporal Resolution in the Auditory Midbrain After Prolonged Deafness Is Reversed by Electrical Stimulation of the Cochlea J Neurophysiol, June 1, 2005; 93(6): 3339 - 3355. [Abstract] [Full Text] [PDF]

				A. Kral, J. Tillein, S. Heid, R. Hartmann, and R. Klinke Postnatal Cortical Development in Congenital Auditory Deprivation Cereb Cortex, May 1, 2005; 15(5): 552 - 562. [Abstract] [Full Text] [PDF]

				J. Syka Plastic Changes in the Central Auditory System After Hearing Loss, Restoration of Function, and During Learning Physiol Rev, July 1, 2002; 82(3): 601 - 636. [Abstract] [Full Text] [PDF]

				M. Vollmer, R. E. Beitel, and R. L. Snyder Auditory Detection and Discrimination in Deaf Cats: Psychophysical and Neural Thresholds for Intracochlear Electrical Signals J Neurophysiol, November 1, 2001; 86(5): 2330 - 2343. [Abstract] [Full Text] [PDF]

				R. L. Snyder, M. Vollmer, C. M. Moore, S. J. Rebscher, P. A. Leake, and R. E. Beitel Responses of Inferior Colliculus Neurons to Amplitude-Modulated Intracochlear Electrical Pulses in Deaf Cats J Neurophysiol, July 1, 2000; 84(1): 166 - 183. [Abstract] [Full Text] [PDF]

				A. Kral, R. Hartmann, J. Tillein, S. Heid, and R. Klinke Congenital Auditory Deprivation Reduces Synaptic Activity within the Auditory Cortex in a Layer-specific Manner Cereb Cortex, July 1, 2000; 10(7): 714 - 726. [Abstract] [Full Text] [PDF]

				R. E. Beitel, R. L. Snyder, C. E. Schreiner, M. W. Raggio, and P. A. Leake Electrical Cochlear Stimulation in the Deaf Cat: Comparisons Between Psychophysical and Central Auditory Neuronal Thresholds J Neurophysiol, April 1, 2000; 83(4): 2145 - 2162. [Abstract] [Full Text] [PDF]

				M. Vollmer, R. L. Snyder, P. A. Leake, R. E. Beitel, C. M. Moore, and S. J. Rebscher Temporal Properties of Chronic Cochlear Electrical Stimulation Determine Temporal Resolution of Neurons in Cat Inferior Colliculus J Neurophysiol, December 1, 1999; 82(6): 2883 - 2902. [Abstract] [Full Text] [PDF]

				R. K. Shepherd, J. H. Baxi, and N. A. Hardie Response of Inferior Colliculus Neurons to Electrical Stimulation of the Auditory Nerve in Neonatally Deafened Cats J Neurophysiol, September 1, 1999; 82(3): 1363 - 1380. [Abstract] [Full Text] [PDF]