Investigating the long term changes in the spinal cord due to neuromuscular electrical stimulation through a dynamic learning mechanism

Authors: I. PEREZ1, *D. S. WON2, L. TONG1, P. ARGUELLO1; 2Electrical Engin., 1California State University, Los Angeles, Los Angeles, CA

Abstract: Recent advancement of computational models of central pattern generator (CPG) spinal circuitry has led to accurate simulation of many characteristics of locomotion. Some of the behaviors that have been achieved include controlling the phases of locomotion (extension or flexion) and coordination of left and right limbs. Achievement of these simulated behaviors is made possible by a 2-level organizational principle of the CPG model: the rhythm generation level generates the intrinsic rhythmic behavior of the spinal cord, and a pattern formation layer is responsible to project the rhythmic behavior as patterns to the motoneurons.

One key characteristic of the spinal circuitry that is of great importance for understanding the process of post-injury rehabilitation but missing from current CPG models is the long term effects of afferent nerve stimulation on synaptic efficacy. Incorporating a learning mechanism for the spinal circuitry model will provide insight to changes of the spinal cord for rehabilitation purposes. The work presented here is framed within the context of developing a neuromuscular electrical stimulation therapy in a rodent model of spinal cord injury.

In order to incorporate the long term effects of neuromuscular electrical stimulation, the spinal circuitry model will incorporate a set of dynamic weights that are dependent on intracellular calcium concentration of the post-synaptic neuron. This type of learning mechanism is based on the modulation of NMDA and AMPA receptors that are responsible for the long term synaptic changes. The influx of calcium ions is known to be a second messenger in the post synaptic neuron for synaptic efficacy. With the addition of the learning mechanism in the spinal circuitry model, changes of the synaptic efficacy due to simulated neuromuscular electrical stimulation are analyzed. In this work, we demonstrate the ability to control the operating point of the dynamic weights, signifying the efficacy of synapses between the afferent Ia fibers and the motoneurons in the CPG, by applying afferent stimulation to the CPG network. These capabilities have implications for studying the capability of using peripheral nerve stimulation to systematically modify and rehabilitate spinal cord locomotor function.

Disclosures: I. Perez: None. D.S. Won: None. L. Tong: None. P. Arguello: None.

The funding for this program is provided by the National Science Foundation under Grant # HRD-1363399.
SfN LINK: Session 059 – Training, Rehabilitation, and Repair: Spinal Cord Injury Recovery

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