P091 Modeling the effects of trans-spinal direct current stimulation on the lumbar spinal circuits

Abstract

Introduction Trans-spinal direct current stimulation (tsDCS) is a potentially new technique for the treatment of Spinal Cord Injury (SCI). The technique aims to alter the response of the neural pathways in the spinal cord, which is hypothesized to have a positive effect on SCI recovery. To establish tsDCS as a possible treatment option for SCI, it is vital to develop a better understanding of its underlying mechanisms to be able to adjust the intervention to the needs of the patient. Objectives We seek to understand the acute polarization effect of tsDCS on the lumbar spinal circuits. Further the question is, if acute, field dependent changes in synaptic efficacy could be used to explain the short term effects reported in previous tsDCS studies. Materials & methods We use a realistic full body segmented finite element model to calculate the electric field inside the spinal cord for three different electrode configurations (DC, 2.5 mA). We apply the calculated electric field to a set of realistic neuron models to investigate changes in membrane resting potential within the neuron as well as afferent and efferent axon terminals. We further make use of a lumbar spinal network model (Cisi et al., 2008) to simulate experimental paradigms used in previous tsDCS studies, with varying synaptic conductivities. The simulation results are correlated with acute, field dependent changes in synaptic efficacy observed in vitro and compared to the effects obtained by other tsDCS studies to date. Results Across electrode configurations, the electric field inside the spinal cord ranged from ∼0.2 V/m to ∼0.6 V/m with a more dominant longitudinal field component (radial/longitudinal 1/3). Across all MN models, axon terminal polarization was dominant ( Conclusion Axon terminal polarization may be a primary contributor to the modulatory effects observed after lumbar tsDCS. However, these longer term effects are opposite to the simulated acute synaptic efficacy changes. This may lead to better methods for predicting the outcome of tsDCS.