Biomedical subjects

Arunkumar N Badi

Publications and source records attributed to Arunkumar N Badi.

3 recordsLinked to original sources

PubMed2007

Electrode independence in intraneural cochlear nerve stimulation.

OBJECTIVES/HYPOTHESIS: We have previously reported feline electrophysiological and anatomical studies focused on the development of an intraneural auditory neuroprosthesis. Because only the tips of the electrodes implanted in the cochlear nerve are the stimulating elements that abut the nerve axons, we hypothesize that intraneural stimulation will be highly focal in nature. In this article, we report the electrophysiological characterization of the selective activation of subpopulations of cochlear nerve fibers via electrodes implanted in feline cochlear nerve. STUDY DESIGN: We have used a forward-masking paradigm to estimate the extent of stimulation overlap produced by pairs of electrodes implanted into the cochlear nerve. METHODS: The technique uses sequential stimulation via masking and probe electrodes and monitoring of the electrically evoked auditory brain stem response as an index of cochlear nerve fiber recruitment. We investigated overlap in all possible electrode pair combinations. RESULTS AND CONCLUSION: Many electrode pairs manifest virtually no overlap in the subpopulations of fibers excited by perithreshold stimuli, whereas most had considerable overlap at higher stimulation levels. However, we also noted that our measured overlap was similar across electrodes possibly because of lack of specificity of the whole nerve electrically evoked auditory brain stem response as an assay for this parameter. These findings indicate that direct cochlear nerve stimulation via intraneural electrodes provides selective excitation of small subpopulations of cochlear nerve fibers, and suggest that cochlear nerve stimulation may selectively evoke narrow-band frequency percepts.

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PubMed2003

Development of a novel eighth-nerve intraneural auditory neuroprosthesis.

OBJECTIVES/HYPOTHESIS: Cochlear nerve stimulation using a linear array of electrodes, the cochlear implant, has become an accepted treatment for profound deafness. Major limitations of this technology are high threshold of stimulation, poor performance in a noisy background, cross-talk between electrodes, unsatisfactory channel selectivity, and variable reconstruction of frequency space. A novel auditory neuroprosthesis is proposed that is expected to overcome these problems by implanting an array of three-dimensional microelectrodes, the Utah Electrode Array, directly into the cochlear nerve. STUDY DESIGN: We have conducted acute, extending for up to 12 hours and semichronic, extending for up to 52 hours, electrophysiological experiments, radiologic and histologic studies in 12 cats. METHODS: The electrically evoked auditory brainstem response was used as a means to characterize the threshold, dynamic range, and stability of cochlear nerve stimulation through the implanted Utah Electrode Array neuroprosthesis. Plain film, computed tomographic, and histological studies were conducted to determine the result of the implant. RESULTS: The electrically evoked auditory brainstem response thresholds were approximately one to two orders of magnitude lower than those evoked with conventional cochlear implants. We were able to close the cochleostomy, bring the cat into normal anatomical position, and obtain stable electrically evoked auditory brainstem responses for up to 52 hours. Plain film and computed tomographic studies indicated that the Utah Electrode Array neuroprosthesis was in the intended position in the nerve. Histological studies did not reveal hemorrhage or significant damage to the nerve. CONCLUSION: Because the presented stimulation paradigm appears to significantly mitigate some of the problems of conventional cochlear implants, it may offer a new therapeutic approach to profound deafness.

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PubMed2002

A technique for implantation of a 3-dimensional penetrating electrode array in the modiolar nerve of cats and humans.

BACKGROUND: We believe that direct intraneural stimulation of the modiolar nerve using an array of electrodes will have lower thresholds, offer greater frequency selectivity and more stimulation sites, and have a greater frequency representation than conventional cochlear implants. OBJECTIVES: To describe a potential auditory prosthesis based on electrical stimulation of the modiolar cochlear nerve and to report the development of a surgical approach in human and animal models. DESIGN: Cadaveric human and animal studies conducted in temporal bones indicated that an array of penetrating microelectrodes could be implanted in the modiolar nerve. Cat studies using anesthesia were performed to develop the surgical procedure in an animal model. Nerve viability was assessed by measurement of electrically evoked auditory brainstem responses at different stages of the surgery. SUBJECTS: Two fresh cadaveric human temporal bones, 3 cat cadavers, 1 pig cadaver, and 6 anesthetized cats were used in the experiments. RESULTS: We were able to implant arrays containing 20 microelectrodes in the human modiolar nerve after exposure by a modified extended facial recess approach. In animals, the modiolar nerve was accessed by the transbulla and the middle fossa approach. The cat was chosen as the appropriate animal model, and the transbulla approach was selected. The round window was exposed by ventral access to the bulla and after cochleostomy; drilling the modiolar bone exposed the modiolar nerve. The mean +/- SD diameter of the exposed nerve in cats was 1.64 +/- 0.07 mm (n = 9), and the mean +/- SD exposed length was 2.50 +/- 0.11 mm (n = 9); this is adequate to accommodate 20 microelectrodes. The electrically evoked auditory brainstem responses indicated nerve survival during and after the surgery. CONCLUSIONS: The surgical technique allows implantation of up to 20 microelectrodes in the cat and human modiolar nerve. The nerve survives the surgical procedure. This work enables studies in the electrophysiological properties and consequences of long-term implantation.

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