Transient optical neural stimulation in vivo

The traditional method of stimulating neural activity has been based on electrical methods and remains the gold standard to date despite inherent limitations. We have developed a new paradigm - transient optical neural stimulation (TONS) to in vivo neural activation based on pulsed infrared light, which provides a contact-free, spatially selective, artifact-free method without incurring tissue damage that may have significant advantages over electrical stimulation in a variety of diagnostic and therapeutic applications. Results demonstrate that low-level laser energy can be used to consistently and reproducibly stimulate action potentials in discrete populations of peripheral nerves with resulting compound nerve and muscle potentials in frogs and rats in vivo with no appreciable tissue damage using radiant exposures well below damage threshold. This phenomenon is wavelength dependent and stimulation threshold follows the inverse of soft tissue absorption. Thus stimulation threshold is a function of the penetration depth of light in tissue. We have developed in conjunction with our industrial partner, an optical stimulator that can be used to stimulate nerves for research purposes. This unit has been shown to successfully stimulate peripheral nerves in vivo in an animal model. Preliminary investigation of the physical mechanism underlying this phenomenon, indicate that TONS is most likely a photo-thermal effect from transient tissue temperature changes resulting in direct or indirect activation of transmembrane ion channels causing propagation of the action potential.