Selective control of electrical neural activation using infrared light

Abstract

The neurostimulation market is one of the fastest growing sectors of the medical device industry. This is primarily due to both an increasing patient population and recent advances in clinical neural interfaces. However, the need for restored neural function remains largely unmet and will require refinements to current technology and development of novel solutions. To fully control neural function and analyze the dynamics of neural circuitry, it is necessary to have tools capable of selectively exciting and inhibiting sub-populations of neurons. Advances in electrical neural interfaces have greatly improved selective stimulation. In addition, electrical methods of blocking nerve conduction have been demonstrated. Recently, a novel optical stimulation technique was developed whereby pulsed infrared light achieves neural activation with spatiotemporal precision. This dissertation investigates the hypothesis that electrical and optical techniques are complimentary and can be cooperatively applied to control neural function. The synergistic combination of pulsed electric current and infrared light is evaluated in a myelinated mammalian nerve, and the methodology is refined through systematic investigation in both unmyelinated and myelinated nerve preparations. This hybrid approach to neurostimulation exhibits spatial specificity of activation while reducing stimulation currents and optical radiant exposures. Infrared light is not only shown to selectively enhance electrical neural excitation, but also to inhibit electrically initiated axonal activation and block propagating action potentials. The utility of this technique is demonstrated through the modulation of neuromuscular function, with the underlying mechanism likely mediated by local infrared-induced changes in baseline nerve temperature. Application of infrared light is shown to selectively enhance and inhibit electrically stimulated muscle activity and contraction force in both unmyelinated and myelinated nerves. The results of this work indicate there is a rich set of interactions between light and excitable tissues, and infrared light can be applied as a multi-faceted tool for selectively controlling neural function for both research and clinical applications.