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