Degradation of temporal resolution in the auditory midbrain after prolonged deafness is reversed by electrical stimulation of the cochlea.
In an animal model of prelingual deafness, we examined the anatomical and physiological effects of prolonged deafness and chronic electrical stimulation on temporal resolution in the adult central auditory system. Maximum following frequencies (Fmax) and first spike latencies of single neurons responding to electrical pulse trains were evaluated in the inferior colliculus of two groups of neonatally deafened cats after prolonged periods of deafness (>2.5 yr): the first group was implanted with an intracochlear electrode and studied acutely (long-deafened unstimulated, LDU); the second group (LDS) received a chronic implant and several weeks of electrical stimulation (pulse rates > or =300 pps). Acutely deafened and implanted adult cats served as controls. Spiral ganglion cell density in all long-deafened animals was markedly reduced (mean <5.8% of normal). Both long-term deafness and chronic electrical stimulation altered temporal resolution of neurons in the central nucleus (ICC) but not in the external nucleus. Specifically, LDU animals exhibited significantly poorer temporal resolution of ICC neurons (lower Fmax, longer response latencies) as compared with control animals. In contrast, chronic stimulation in LDS animals led to a significant increase in temporal resolution. Changes in temporal resolution after long-term deafness and chronic stimulation occurred broadly across the entire ICC and were not correlated with its tonotopic gradient. These results indicate that chronic electrical stimulation can reverse the degradation in temporal resolution in the auditory midbrain after long-term deafness and suggest the importance of factors other than peripheral pathology on plastic changes in the temporal processing capabilities of the central auditory system.
Vollmer
Maike
M
Dept. of Otolaryngology-HNS, Epstein Laboratory, University of California San Francisco, 513 Parnassus Ave., U-490, San Francisco, CA 94143-0526, USA. vollmer@itsa.ucsf.edu
Leake
Patricia A
PA
Beitel
Ralph E
RE
Rebscher
Stephen J
SJ
Snyder
Russell L
RL
D000161:Acoustic Stimulation / Q000379:methods; D000200:Action Potentials / Q000502:physiology; D000818:Animals; D000831:Animals, Newborn; D001309:Auditory Threshold / Q000502:physiology / Q000528:radiation effects; D002415:Cats; D002452:Cell Count / Q000379:methods; D003051:Cochlea / Q000473:pathology / Q000528:radiation effects*; D003054:Cochlear Implants; D003638:Deafness / Q000473:pathology* / Q000503:physiopathology; D004195:Disease Models, Animal; D004307:Dose-Response Relationship, Radiation; D004558:Electric Stimulation; D007245:Inferior Colliculi / Q000473:pathology* / Q000503:physiopathology; D009474:Neurons / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology / Q000528:radiation effects; D013136:Spiral Ganglion / Q000473:pathology / Q000528:radiation effects; D018709:Statistics, Nonparametric; D013997:Time Factors