Studying the effects of long term changes of neuromuscular electrical stimulation through a spinal circuitry model

Various forms of neural stimulation have been shown to produce enhancements in locomotor behavior in spinal cord injured subjects, and the importance of afferent feedback has been implicated in the rehabilitive effects of peripheral nerve stimulation. However, the extent to which such behavioral modifications are observed vary widely and the mechanism behind these changes are yet to be elucidated. Much progress has been previously made in the field of computational modeling, and in particular in the modeling of central pattern generator circuitry responsible for producing rhythmic locomotor output. However, even the most advanced models still lack a mechanism for lasting rehabilitative modifications of spinal circuitry. We focus our efforts on incorporating a mode by which afferent feedback induces lasting changes in motoneuron synaptic weight. We demonstrate that by incorporating the calcium control hypothesis into our CPG model, afferent feedback can shift the operating point in post-synaptic calcium concentration, which in turn leads to changes in synaptic weight which last beyond the period of afferent stimulation.