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Microstimulation of primary afferent neurons in the L7 dorsal root ganglia using multielectrode arrays in anesthetized cats: thresholds and recruitment properties

R A Gaunt1, J A Hokanson2 and D J Weber1,2

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Current research in motor neural prosthetics has focused primarily on issues related to the extraction of motor command signals from the brain (e.g. brain–machine interfaces) to direct the motion of prosthetic limbs. Patients using these types of systems could benefit from a somatosensory neural interface that conveys natural tactile and kinesthetic sensations for the prosthesis. Electrical microstimulation within the dorsal root ganglia (DRG) has been proposed as one method to accomplish this, yet little is known about the recruitment properties of electrical microstimulation in activating nerve fibers in this structure. Current-controlled microstimulation pulses in the range of 1–15 µA (200 µs, leading cathodic pulse) were delivered to the L7 DRG in four anesthetized cats using penetrating microelectrode arrays. Evoked responses and their corresponding conduction velocities (CVs) were measured in the sciatic nerve with a 5-pole nerve cuff electrode arranged as two adjacent tripoles. It was found that in 76% of the 69 electrodes tested, the stimulus threshold was less than or equal to 3 µA, with the lowest recorded threshold being 1.1 µA. The CVs of afferents recruited at threshold had a bimodal distribution with peaks at 70 m s−1 and 85 m s−1. In 53% of cases, the CV of the response at threshold was slower (i.e. smaller diameter fiber) than the CVs of responses observed at increasing stimulation amplitudes. In summary, we found that microstimulation applied through penetrating microelectrodes in the DRG provides selective recruitment of afferent fibers from a range of sensory modalities (as identified by CVs) at very low stimulation intensities. We conclude that the DRG may serve as an attractive location from which to introduce surrogate somatosensory feedback into the nervous system.


PACS

87.80.-y Biophysical techniques (research methods)

87.19.R- Mechanical and electrical properties of tissues and organs

87.85.J- Biomaterials

87.19.lt Sensory systems: visual, auditory, tactile, taste, and olfaction

87.19.L- Neuroscience

Subjects

Instrumentation and measurement

Medical physics

Biological physics

Dates

Issue 5 (October 2009)

Received 19 December 2008, accepted for publication 20 April 2009

Published 1 September 2009



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