Application of infrared light for in vivo neural stimulation

Abstract

A novel method for damage-free, artifact-free stimulation of neural tissue using pulsed, low-energy infrared laser light is presented. Optical stimulation elicits compound nerve and muscle potentials similar to responses obtained with conventional electrical neural stimulation in a rat sciatic nerve model. Stimulation and damage thresholds were determined as a function of wavelength using a tunable free electron laser source (lambda = 2 to 10 microm) and a solid state holmium:YAG laser (lambda = 2.12 microm). Threshold radiant exposure required for stimulation varies with wavelength from 0.312 Jcm2 (lambda = 3 microm) to 1.22 Jcm2 (lambda = 2.1 microm). Histological analysis indicates no discernable thermal damage with suprathreshold stimulation. The largest damage/stimulation threshold ratios (>6) were at wavelengths corresponding to valleys in the IR spectrum of soft tissue absorption (4 and 2.1 microm). Furthermore, optical stimulation can be used to generate a spatially selective response in small fascicles of the sciatic nerve that has significant advantages (e.g., noncontact, spatial resolution, lack of stimulation artifact) over conventional electrical methods in diagnostic and therapeutic procedures in neuroscience, neurology, and neurosurgery.

Optical stimulation enables paced electrophysiological studies in embryonic hearts

“…These include the time and cost required to perform genetic manipulations, the potential that the added ion channels may alter the electrical properties of the cells, the decreased responsiveness to light with repeated stimulation [38], and the likelihood of triggering an action potential when the light-sensitive channels are exposed to the optical mapping excitation light due to overlap of the excitation spectra [39,40] and much lower power requirements necessary for exciting the channels [41]. Infrared stimulation does have the potential to damage tissue if too much heat is deposited, but previously published results suggest that infrared stimulation can be used without damage [24][25][26][27][28][29][30][33][34][35]. Similarly, in this study, no functional damage was observed, as the pacing threshold did not increase over the course of an experiment.…”

“…Most other studies using infrared stimulation have also been conducted with multimode fibers [24][25][26][27][28][29][30][31][32][33][34][35]. However, it is extremely challenging to focus light from a multimode fiber to a spot size smaller than the fiber core diameter.…”

“…Second, since optical pacing works through a heat deposition mechanism, no areas of potentially damaging high charge densities are generated. While heat can damage tissue, previous studies indicate that the stimulation threshold is below the thermal damage threshold [24][25][26][27][28][29][30][33][34][35]. Third, optical pacing does not inject current, avoiding the electrical artifact created by electrode pacing.…”

“…Infrared stimulation was first developed in nerves [24] and has been used to stimulate a variety of nerves and neurons [25][26][27][28][29][30], vestibular hair cells [31], and isolated myocytes [32] using multimode fibers. Additionally, we have recently demonstrated the use of infrared stimulation to optically pace whole intact embryonic [33] and adult hearts [34].…”

Multimodal Neuroimaging Microtool for Infrared Optical Stimulation, Thermal Measurements and Recording of Neuronal Activity in the Deep Tissue

“…Infrared neural stimulation (INS) is an emerging method, first presented by Wells et al in 2005 [1]. Spatially controlled short pulses of infrared light are used to modulate neuronal activity without molecular intervention or sensitization.…”