Infrared neural stimulation of Aplysia californica

Abstract

Infrared neural stimulation (INS) has been shown to induce neural activity with spatial selectivity without inducing a stimulation artifact or necessitating tissue contact. Most experiments with this technology have been done in mammals, but much is still unknown about INS. Characterization of the experimentally tractable nervous system of the marine mollusk, Aplysia californica, will allow us to answer fundamental questions. In these studies, INS feasibility in Aplysia is shown and characterized with respect to repetition rate, pulse duration, wavelength and temperature. Nerve recordings were taken while stimulating buccal nerve 3 of the buccal ganglion using pulsed infrared light. At each parameter value, the nerve was stimulated at a random radiant exposure level (J/cm2), and observation of stimulation was reported. Stimulation thresholds were calculated as the effective dose (ED50) outputted by a probit regression. No change in stimulation thresholds were investigated at laser repetition rates ranging between 0.5-15 Hz. Stimulation at pulse durations ranging from 3-10 ms showed no change in threshold while it decreased below and increased above that range. Studies showed that a wavelength of 1.875 μm was more efficient for inducing action potentials than at 1.865 μm. Investigations of the ambient temperature challenged previous work by showing that at lower temperatures (0 Celsius) the threshold increased. Complex behavioral patterns were induced using INS in neural networks providing new directions for future clinical devices. Having shown feasibility in Aplysia, we believe this is a useful model for further studies on the physiological mechanism and optimal laser parameters of INS.