Plastic Surgery Research Council
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PSRC 60th Annual Meeting
Program and Abstracts

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Development of a Brain Body Interface for Upper Limb Reanimation: Selective Muscle Activation with a Chronically Implanted Nerve Cuff Electrode on the Sciatic Nerve
Neil Fairbairn, MD1, Wasim Q. Malik, PhD2, Neelakantan Sunder, MD1, Robert Ajemian, PhD2, Ashley Turza, PhD2, Victoria Vega, PhD2, Jeena Easow, MD1, Emilio Bizzi, MD, PhD2, Emory Brown, MD, PhD2, Jonathan M. Winograd, MD1.
1Massachusetts General Hospital, Boston, MA, USA, 2Massachusetts Institute of Technology, Cambridge, MA, USA.

PURPOSE:Spinal cord injury results in devastating loss of motor control. However, cortical signals of motor intention above the injury, and lower motor neurons below remain intact. Currently, brain-machine interface (BMI) systems, which rely on implanted cortical electrodes to control the movment of an artificial limb or computer cursor, have demonstrated the potential to bypass injury and return lost motor function. We propose that a brain-body interface (BBI), where cortical signals are fed directly into paralyzed muscles, may offer some distinct advantages over BMI. This approach acknowledges current limited understanding of cortical representation and instead aims to harness the brain’s plasticity in order to re-organize neural connections and “re-learn” how to move the limb. Our overarching aim is to demonstrate restoration of voluntary motor function in a non-human primate (NHP) using cortically driven functional electrical stimulation (FES) of peripheral nerves with implantable nerve cuff electrodes. We have developed a highly selective, reversible paralysis model to simulate spinal cord injury in the upper extremity in a NHP. The aim of this portion of the study was to demonstrate selective fascicular stimulation of murine and rodent sciatic nerves using acute and chronically implanted, polyamide nerve cuff electrodes in preparation for implantation into the NHP spinal cord injury model. The NHP model will require the placement of the electrodes on small nerve branches (1-2mm) analogous in size to the rodent sciatic nerves.
METHODS:8-channel polyamide stimulating cuff electrodes were wrapped around the sciatic nerves of adult Sprague Dawley rats (n=5) and C57 Black 6 mice (n=5). Cuff electrodes were connected to a Tucker-Davies stimulation/recording system. Electromyography (EMG) needle electrodes were inserted into the tibialis anterior (TA) and gastrocnemius (G) muscles to record muscle activity. Single pulses and pulse trains were delivered to the various channels of the cuff while pulse parameters, including pulse amplitude and width, were systematically varied. Following successful demonstration of selective fascicular stimulation in non-survival surgeries, stimulating nerve cuff electrodes and EMG recording electrodes were implanted chronically in the rat to assess the stability of the equipment.
RESULTS:Muscle activity was recorded in all animals. In 9 animals, we successfully obtained muscle recruitment curves as a function of stimulation amplitude. Depending on channel activation, we were able to show selective activation of tibial and common peroneal fascicles and therefore selective recruitment of G and TA muscles respectively. Following 30 days of chronic implantation in the rat, successful selective stimulation and recording was still possible.
CONCLUSION:We have successfully shown that selective fascicular stimulation can be achieved using implantable cuff electrodes in sub-1mm nerves and over prolonged periods. Following implantation of an epicortical recording array in the NHP, we intend to use these nerve cuffs to deliver cortically recorded signals of motor intention directly to peripheral nerves of the upper limb. By activating this system during reversible paralysis achieved with selective nerve blocks, we aim to show that, through mechanisms of cortical learning and plasticity, the NHP is able to regain control of limb movement.


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