Spatial Selectivity to Intracochlear Electrical Stimulation in the Inferior Colliculus is Degraded After Long-Term Deafness in Cats

Abstract

Vollmer M, Beitel RE, Snyder RL, Leake PA. Spatial selectivity to intracochlear electrical stimulation in the inferior colliculus is degraded after long-term deafness in cats. J Neurophysiol 98: 2588 -2603, 2007. First published September 12, 2007 doi:10.1152/jn.00011.2007. In an animal model of electrical hearing in prelingually deaf adults, this study examined the effects of deafness duration on response thresholds and spatial selectivity (i.e., cochleotopic organization, spatial tuning and dynamic range) in the central auditory system to intracochlear electrical stimulation. Electrically evoked auditory brain stem response (EABR) thresholds and neural response thresholds in the external (ICX) and central (ICC) nuclei of the inferior colliculus were estimated in cats after varying durations of neonatally induced deafness: in animals deafened Ͻ1.5 yr (short-deafened unstimulated, SDU cats) with a mean spiral ganglion cell (SGC) density of ϳ45% of normal and in animals deafened Ͼ2.5 yr (long-deafened, LD cats) with severe cochlear pathology (mean SGC density Ͻ7% of normal). LD animals were subdivided into unstimulated cats and those that received chronic intracochlear electrical stimulation via a feline cochlear implant. Acutely deafened, implanted adult cats served as controls. Independent of their stimulation history, LD animals had significantly higher EABR and ICC thresholds than SDU and control animals. Moreover, the spread of electrical excitation was significantly broader and the dynamic range significantly reduced in LD animals. Despite the prolonged durations of deafness the fundamental cochleotopic organization was maintained in both the ICX and the ICC of LD animals. There was no difference between SDU and control cats in any of the response properties tested. These findings suggest that long-term auditory deprivation results in a significant and possibly irreversible degradation of response thresholds and spatial selectivity to intracochlear electrical stimulation in the auditory midbrain.

Behavioral training restores temporal processing in auditory cortex of long-deaf cats

“…Some of the experimental procedures have been described in detail in previous reports (e.g., Beitel et al 2000aBeitel et al , 2011Schreiner and Raggio 1996;Snyder et al 1995;Vollmer et al 2001Vollmer et al , 2007 and will be repeated here in an abbreviated form. All surgical and experimental procedures were approved by the Institutional Animal Care and Use Committee of the University of California, San Francisco and conformed to the guidelines of the National Institutes of Health for the care and use of laboratory animals.…”

Chronic electrical stimulation does not prevent spiral ganglion cell degeneration in deafened guinea pigs

“…Cochlear hair cell loss also leads to morphological and functional changes in central parts of the auditory system. These occur among others in the large axosomatic endings of the auditory nerve in the cochlear nucleus (Ryugo et al, 2010) and in its projection (Leake et al, 2006), as well as in the inferior colliculus (Vollmer et al, 2007) and auditory cortex (Ryugo et al, 1995;Kral and Tillein, 2006). These changes may in turn enhance the degeneration of SGCs since, besides afferent connections from hair cells, efferent connections from higher centers are thought to play a role in SGC survival (e.g., Hegarty et al, 1997).…”

An anatomical assessment of the supracerebellar midline and paramedian approaches to the inferior colliculus for auditory midbrain implants using a neuronavigation model on cadaveric specimens

“…Early studies in animals demonstrated a strong correlation between the laminar organization of neurons and the tonotopic geometry of the IC. 18,19 Morest and Oliver showed that the IC consists of neural layers analogous to those observed across different species. 14 These layers correspond to different frequency laminae and justified a closer examination of the surgical challenges reaching the IC and positioning an auditory prosthesis.…”