Cochlear Implant Research in the Epstein Laboratory addresses fundamental issues related to the development, safe application and effects of stimulation with multichannel cochlear prostheses. The goal of this work is to provide a better understanding of the anatomical and functional changes which occur after deafness, especially when hearing loss occurs early in life, and to determine the consequences of electrical stimulation with a cochlear implant applied during development, using models of current prosthetic devices being applied in profoundly deaf people. This research is supported by an NIH Contract from the National Institute on Deafness and Other Communication Disorders, Contract #N01-DC-7-2105, "Protective Effects of Patterned Electrical Stimulation on the Deafened Auditory System" and the Epstein Fund. Click here for a list of current publications.

* Research has demonstrated that chronic electrical stimulation of the cochlea can prevent the degeneration of the cochlear neurons that otherwise occurs as a consequence of deafness. Moreover, higher frequency, complex stimulation is more effective than low frequency signals in inducing these protective effects.

A. Deaf, Stimulated
B. Deaf, Unstimulated

* The functional consequences of electrical stimulation delivered by a cochlear implant also have been examined by studies of the response properties of single neurons within the auditory midbrain. Results indicate that the frequency organization of the central auditory system is relatively normal for many months after deafness occurring early in life. In contrast, chronic stimulation of a single channel of a cochlear implant causes marked expansion of its representation and consequent distortion in the frequency map. Parallel alterations in the temporal response properties to electrical stimulation also have been demonstrated.

* Research continues on developing improved designs for multichannel cochlear implants. In order to evaluate novel electrode designs, a clear plastic model of the human cochlea has been developed which contains a dimensionally accurate replica of the scala tympani. This research tool allows the surgeon or engineer to directly observe the insertion of cochlear implant electrodes, and to assess how the mechanical properties of the electrode might affect the safety and accuracy of surgical placement. The model is currently being used here at UCSF, and at several other cochlear implant research centers throughout the world, to develop improved electrodes, surgical techniques and instruments.

Basic Anatomical and Developmental Studies of the Cochlea and Its Neural Projections to the Cochlear Nucleus.

A second research project focuses on unresolved questions about the fundamental organization of the neural connections from the mammalian cochlea, to the first (and obligatory) synaptic relay nucleus in the brainstem, the cochlear nucleus. We have used a variety of electrophysiological, morphometric, ultrastructural and cytochemical labeling techniques to examine the detailed frequency organization of these projections. Recent studies seek to determine how and when this organization is established during development and how deafness effects these pathways. This work is supported by an NIH Grant entitled "Morphology and Connections of the Spiral Ganglion" #RO1 DC00160 and Hearing Research Inc. Click here for a list of current publications.

* Cytochemical labeling techniques have been used to define the complex organization of the cochlear projections to the brainstem with resolution not previously possible. These studies demonstrated a previously unrecognized anatomical organization of the spiral ganglion. That is, in addition to the orderly representation of frequency along the spiral axis of the ganglion, there is also a systematic representation of the vertical dimension of the ganglion across the "isofrequency laminae" within the cochlear nucleus.

* Ultrastructural studies have examined the spatial distribution of synapses on inner hair cells in serial section TEM analyses. Results indicate a selective distribution of high-and low-spontaneous rate auditory nerve inputs across the isofrequency laminae of the cochlear nucleus.

* Most recently, we have studied the postnatal development of these highly organized cochlear projections. This work has revealed that auditory nerve projections to the dorsal and posteroventral divisions of the cochlear nucleus are nearly adult-like at birth, but collaterals of these same axons to the anteroventral division undergo substantial refinement postnatally.