Effect of sensory and optical stimulation on M-/H-reflex and population excitatory post-synaptic potential (pEPSP).

<p>(<b>A</b>) Schematics of the experimental set-up. Extracellular recordings were performed during stimulation of the sciatic nerve. Electrical stimulation of the sciatic nerve evoked both a population EPSP in the spinal cord and a M-/H- reflexes in the muscle. (<b>B</b>) pEPSPs were recorded at different depths by means of a linear array (see Methods). On the left, it is shown the position of stimulation of the spinal cord with respect to the recording electrodes (reported as rows on the right). On the right, the three columns represent respectively the effect of the pEPSP evoked by electrical stimulation (of the sciatic nerve), by combining electrical and optical stimulation, and AUROC indices (see Methods) to quantify the differences with vs. without optical activation. Population potentials at different depths were mostly perturbed when light was applied at the same position and marginally when it was in the proximity (about 2 mm) of the recording electrode. No difference was present when the light was shined at greater distances from the recording electrode. (<b>C</b>) Electromyography activity evoked by combining electrical stimulation of the sciatic nerve with (blue) and without (black) optical stimulation at different position of the spinal cord. Zero distance indicates that light was shone at the same position of the recording electrodes. No effect of the light stimulation on neither M- nor H- reflexes (p>0.05, sign-rank test) was observed independently on the position of the light.