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Limb-state feedback from ensembles of simultaneously recorded dorsal root ganglion neurons

D J Weber1, R B Stein2, D G Everaert2 and A Prochazka2

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Functional electrical stimulation (FES) holds great potential for restoring motor functions after brain and spinal cord injury. Currently, most FES systems are under simple finite state control, using external sensors which tend to be bulky, uncomfortable and prone to failure. Sensory nerve signals offer an interesting alternative, with the possibility of continuous feedback control. To test feasibility, we recorded from ensembles of sensory neurons with microelectrode arrays implanted in the dorsal root ganglion (DRG) of walking cats. Limb position and velocity variables were estimated accurately (average R2 values >0.5) over a range of walking speeds (0.1–0.5 m s−1) using a linear combination of firing rates from 10 or more neurons. We tested the feasibility of sensory control of intraspinal FES by recording from DRG neurons during hindlimb movements evoked by intraspinal microstimulation of the lumbar spinal cord in an anesthetized cat. Although electrical stimulation generated artifacts, this problem was overcome by detecting and eliminating events that occurred synchronously across the array of microelectrodes. The sensory responses to limb movement could then be measured and decoded to generate an accurate estimate of the limb state. Multichannel afferent recordings may thus provide FES systems with the feedback needed for adaptive control and perturbation compensation, though long-term stability remains a challenge.


PACS

87.80.-y Biophysical techniques (research methods)

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

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

87.19.rs Movement

87.19.L- Neuroscience

Subjects

Instrumentation and measurement

Medical physics

Biological physics

Dates

Issue 3 (September 2007)

Received 30 January 2007, accepted for publication 13 July 2007

Published 22 August 2007



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