The excitatory effect of temperature on the Hodgkin-Huxley model

Neurostimulation has emerged as an effective means of treating a wide range of neurological disorders. Recent work has shown that precise delivery of infrared stimulation can modulate neural activity in a reversible manner. A possible mechanism underlying the excitatory effect of infrared stimulation is a localized elevation of temperature. To gain insight into how small elevations in temperature could potentially modulate neural activity, we explored the temperature sensitivity of the well-established Hodgkin-Huxley computational model of the squid giant axon. We relied on experimentally-derived temperature coefficients, or Q10 values, associated with gating kinetics for all the underlying currents and the maximum conductances, as well as the inherent temperature dependence of the equilibrium potentials of the ion conductances. While temperature elevations alone failed to induce action potentials in the computational model, small increases in temperature modulated the firing rate during constant current injection where greater than 30% increase in spike rate was observed with 2°C elevation in temperature. Furthermore, we observed that the rise in spike rate was largely due to the predicted temperature sensitivity of rate constants that form the basis of the gating parameters of the Hodgkin-Huxley computational model. Our findings suggest that the known biophysics of ion conductances may account, at least in part, for the excitatory effects of thermal elevations induced by exposure to infrared stimulation