Hybrid electro-optical stimulation of the rat sciatic nerve induces force generation in the plantarflexor muscles

Abstract

Objective Optical methods of neural activation are becoming important tools for the study and treatment of neurological disorders. Infrared nerve stimulation (INS) is an optical technique exhibiting spatially precise activation in the native neural system. While this technique shows great promise, the risk of thermal damage may limit some applications. Combining INS with traditional electrical stimulation, a method known as hybrid electro-optical stimulation, reduces the laser power requirements and mitigates the risk of thermal damage while maintaining spatial selectivity. Here we investigate the capability of inducing force generation in the rat hind-limb through hybrid stimulation of the sciatic nerve. Approach Hybrid stimulation was achieved by combining an optically transparent nerve cuff for electrical stimulation and a diode laser coupled to an optical fiber for infrared stimulation. Force generation in the rat plantarflexor muscles was measured in response to hybrid stimulation with 1-second bursts of pulses at 15 and 20 Hz and with a burst frequency of 0.5 Hz. Main Results Forces were found to increase with successive stimulus trains, ultimately reaching a plateau by the 20th train. Hybrid evoked forces decayed at a rate similar to the rate of thermal diffusion in tissue. Preconditioning the nerve with an optical stimulus resulted in an increase in the force response to both electrical and hybrid stimulation. Histological evaluation showed no signs of thermally induced morphological changes following hybrid stimulation. Our results indicate that an increase in baseline temperature is a likely contributor to hybrid force generation. Significance Extraneural INS of peripheral nerves at physiologically relevant repetition rates is possible using hybrid electro-optical stimulation.

Infrared neural stimulation of primary visual cortex in non-human primates

“…4 suggest functional activation of underlying neural circuitry associated with ocular dominance, orientation domains, and/or color domains. This is an exciting finding suggesting that INS can be used to selectively activate neuronal circuitry if targeted properly (Lu and Roe, 2008), and this high degree of spatial precision is consistent with other applications of INS that have reported spatially precise evoked neural activity (Cayce et al, 2011; Duke et al, 2012a, 2012b; Feng et al, 2010; Jenkins et al, 2010; Katz et al, 2010; Richter and Matic, 2012; Wells et al, 2007b). Furthermore, the time course of the INS evoked OIS in Fig.…”

“…The heat gradient responsible for evoking neural activity has consistently been identified as a concern for its potential in causing damage to neural tissue (Cayce et al, 2011; Duke et al, 2012b; Goyal et al, 2012; Teudt et al, 2007; Wells et al, 2007c). While a comprehensive damage study was not possible in these experiments, INS was performed in the same animal over the course of a year with no apparent signs of damage.…”

Biological effects and medical applications of infrared radiation

“…Recently, a hybrid electro-optical stimulation technique has been developed to combine INS with electrical stimulation [59, 60]. The sciatic nerve of the rat hind-limb was irradiated by a pulsed diode laser (λ = 1875 nm) during electrical stimulation.…”

Target structures for cochlear infrared neural stimulation

“…In other words, if it is possible to change the resting potential of the neuron toward the activation threshold for sodium channels, the neuron becomes more sensitive to optical stimulation. It has been shown in oocytes, 9 in Aplysia californica and in rat sciatic nerves, 36,37 that the threshold for INS can be lowered by electrical-optical costimulation. The electrical stimulus is thought to depolarize the cell without evoking an action potential.…”