A Setup for Conduction Velocities and Temperature Gradients Measurements during Infrared Neurostimulation

Abstract

Infrared Neural Stimulation (INS) is a novel neuromodulation technique involving a rapid temperature increase of the neuron membrane, resulting in action potential triggering. This paper describes an experimental setup developed to measure the spatiotemporal temperature gradients at the surface of an ex vivo sciatic nerve. The setup is also designed to measure the conduction velocity of the nervous fibers excited by INS, with the aim of determining the type of fibers activated during optical stimulation. Two animal experiments successfully validated the setup and provided encouraging results on (1) the impact of heat accumulation on INS and (2) the difference in nerve fibers excited by optical and electrical nerve stimulation.

Heat accumulation during infrared stimulation impacts the response of ex vivo rat sciatic nerve*

“…Electrical stimulation was repeated between each optical stimulation to verify the integrity of the nerve and the absence of functional damage induced by the optical stimulation. In our previous experiments, a sensitization effect was observed at a stimulation rate of 10 Hz [13], [15]. In this study, lower (5 Hz, 7.7 Hz) and higher (12.5 Hz, 20 Hz) stimulation rates were used to investigate the effect of repetition rate on sensitization and to determine how heat accumulation affects the CNAP elicitation.…”

“…A thermal camera captures the sciatic nerve sample surface to monitor the spatiotemporal temperature gradients induced by INS. The experimental setup used for the experiments is extensively detailed in [15].…”

“…The amplified output is digitized at a 40 kHz sampling frequency by a DAQ (USB-6212, National Instrument Corp., USA) and processed using MATLAB (MathWorks, Natick, USA). This recording setup is described in more details and has been used in [13], [15]- [17].…”

“…The stimulator generates biphasic square current pulses (negative pulse of 0.2 ms, then an interphase delay of 10 µs, and finally a recovery pulse of 0.2 ms with opposite amplitude) ranging from 10 to 500 µA. The same electrical stimulator has been used in [13], [15].…”

“…The experiments were conducted on rat sciatic nerves, excised from male Wistar rats according to the procedure detailed in [13], [15] and in agreement with the ETS 123 European Convention.…”