Elsevier

Hearing Research

Volume 198, Issues 1–2, December 2004, Pages 48-58
Hearing Research

Feasibility of using silicon-substrate recording electrodes within the auditory nerve

https://doi.org/10.1016/j.heares.2004.07.009Get rights and content

Abstract

The use of penetrating, silicon-substrate (i.e., “thin-film”) probes within a cross-section of a sensory nerve offers the possibility of assessing the pattern and extent of fiber excitation within the nerve. We used acute cat preparations to assess the feasibility of this technique for recordings within the auditory nerve trunk. Four probe configurations fabricated by the University of Michigan Center for Neural Communication Technology were evaluated using acoustic and electric stimuli. Our main concerns were the nature of the recorded potentials and the degree of spatial selectivity provided by these probes. We also made some basic assessments of electrode-tissue compatibility. The recorded potentials were characterized as field potentials with varying degrees of spatial selectivity. In some cases, responses to pure tones demonstrated good spatial selectivity, with unique responses recorded by different electrode sites. When electrode sites were positioned at different longitudinal positions along the nerve trunk, responses with latencies characteristic of each site were recorded. These results indicate that thin-film electrodes are capable of providing spatially specific response information from sensory nerves. However, in the case of feline auditory nerves, place-specific responses were inconsistently observed, making it difficult to use this technique to obtain detailed cochleotopic maps of neural excitation. More productive results may be possible from other peripheral nerves with less complex spatial arrangements of fibers.

Introduction

Silicon-based multichannel thin-film microprobes can be used to record single- and multi-unit activity from the cortex and brainstem nuclei, providing spatially specific responses from multiple neural sites (Drake et al., 1988; Arenberg et al., 2000; Bierer et al., 2002). A potential application of thin-film probes is the recording of activity from sites within peripheral nerves. For example, measurement of fiber activation patterns in the mammalian auditory nerve could provide information about excitation patterns produced by intracochlear electrode arrays for prosthetic stimulation of the auditory system. There are distinct advantages in recording neural activity at the periphery of a sensory system. The confounding influence of convergent or descending neural circuits may be reduced, as may anesthesia effects. Also, nerve responses provide temporal response data that may be difficult to capture at central sites. Finally, as they arise from an obligatory pathway, peripheral responses provide information regarding the neural representation of stimuli available to the central nervous system.

The work described here sought to determine the feasibility of using thin-film probes to record spatial excitation patterns within the mammalian auditory nerve. Provided by the University of Michigan’s Center for Neural Communication Technology (CNCT), these silicon-based probes consist of one or more penetrating shanks, each with multiple electrode sites. As they have not previously been used in auditory nerve research, our efforts involved determining the utility of existing designs and new probes tailored to the feline auditory nerve.

Section snippets

Goals of this study

An initial goal of this study was to identify thin-film probes that could be successfully inserted into the cat auditory nerve trunk. This would require experimentation with existing designs to determine compatible dimensions and an assessment of tissue damage secondary to insertion. We then sought to characterize the nature of the evoked potentials recorded by such probes. While thin-film probe recordings of CNS sites can yield single- or multi-unit potentials (Drake et al., 1988; Arenberg et

Animal preparation

Eight adult cats were used in acute, non-survival sessions. This species was chosen because its auditory physiology is the most thoroughly described and its cranial anatomy provides adequate access for inserting thin-film probes into the nerve trunk. Surgical procedures were similar to those of Miller et al. (1998). Briefly, a sedative of ketamine (30 mg/kg) and xylazine (0.3 mg/kg) was administered, followed by atropine sulfate (0.04 mg/kg/12 h, s.q.) to reduce mucosal secretions. The femoral

Mechanical compatibility and tissue damage

Preliminary work with two cats made clear that electrode shanks with widths greater than 40 μm could not be inserted into a plane orthogonal to the nerve axis without large compressive deformation of the nerve. Also, a probe tip angle less than or equal to 20° was found to ease insertion. We selected two single-shank probes with appropriate dimensions: the NASA1 and the PSU4 designs. In the first case (subject C86), a PSU4 single-shank probe was inserted only once in a plane orthogonal to the

Discussion

Our study indicates that it is feasible to use thin-film probes within the auditory nerve, but with mixed results. On the positive side, we found that electrodes of appropriate dimensions could be inserted into the nerve with little gross trauma to the nerve. Insertion was aided by a narrow angle (<20°) of the tip shank and relatively small (<50 μm) shank widths. We note that our examination of insertion trauma was limited to short durations of insertion typical of acute animal studies;

Acknowledgements

This work was supported by NIH contract N01-DC-9-2107. The silicon probes were provided by the University of Michigan Center for Neural Communications Technology, supported by NIH NIBIB grant P41-RR09754.

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