Infrared neural stimulation of thalamocortical brain slices in vitro

Abstract

Neural stimulation using infrared light has recently been characterized as a novel method to stimulate peripheral nerves without touching, causing damage, or inducing an electrical stimulation artifact. Infrared neural stimulation (INS) has not been previously achieved in the brain due to the complexity of the neuronal networks. The purpose of this study was to show feasibility of INS in the central nervous system, and determine the optimal parameters for INS in a thalamocortical brain slice model. Wavelength was the first parameter identified since previous studies showed penetration depth of light in tissue determined the threshold radiant energies needed to evoke an action potential in the peripheral nervous system. The wavelength of 3.65 µm was determined to be the optimal wavelength. Next repetition rate was investigated using the optimal wavelength of 3.65 µm. Lower threshold radiant energies were observed for higher repetition rates. The final parameter investigated was spot size using light at 3.65 µm and 30 Hz, and a third order power fit relationship was observed where a larger spot size required less energy to evoke action potentials in a TC slice. A small set of experiments were performed to show intracellular electrical recordings could be used to detect INS evoked signals. The results from this study prove feasibility of INS in CNS, and provide the basis for future in vivo experiments.