Infrared neurostimulation in ex-vivo rat sciatic nerve using 1470 nm wavelength

Abstract

Objective. To design and implement a setup for ex-vivo optical stimulation for exploring the effect of several key parameters (optical power and pulse duration), activation features (threshold, spatial selectivity) and recovery characteristics (repeated stimuli) in peripheral nerves. Approach. A nerve chamber allowing ex-vivo electrical and optical stimulation was designed and built. A 1470 nm light source was chosen to stimulate the nerve. A photodiode module was implemented for synchronization of the electrical and optical channels. Main results. Compound neural action potentials (CNAPs) were successfully generated with infrared light pulses of 200–2000 µs duration and power in the range of 3–10 W. These parameters determine a radiant exposure for stimulation in the range 1.59–4.78 J cm−2. Recruitment curves were obtained by increasing durations at a constant power level. Neural activation threshold is reached at a mean radiant exposure of 3.16 ± 0.68 J cm−2 and mean pulse energy of 3.79 ± 0.72 mJ. Repetition rates of 2–10 Hz have been explored. In eight out of ten sciatic nerves (SNs), repeated light stimuli induced a sensitization effect in that the CNAP amplitude progressively grows, representing an increasing number of recruited fibres. In two out of ten SNs, CNAPs were composed of a succession of peaks corresponding to different conduction velocities. Significance. The reported sensitization effect could shed light on the mechanism underlying infrared neurostimulation. Our results suggest that, in sharp contrast with electrical stimuli, optical pulses could recruit slow fibres early on. This more physiological order of recruitment opens the perspective for specific neuromodulation of fibre population who remained poorly accessible until now. Short high-power light pulses at wavelengths below 1.5 µm offer interesting perspectives for neurostimulation.

Action Potential Detection Algorithm Adaptable to Individual Nerve and Recording Setup

“…We proposed an action potential detection algorithm with a versatile template matching and validated it with an acute VENG analysis. It was developed as part of the investigations performed by our group in neural data processing [4], [14], [17], [18], [23], [24]. The algorithm is fully automated, and default parameters are proposed.…”

Modulation of neuronal dynamics by sustained and activity-dependent continuous-wave near-infrared laser stimulation

“…This supports previous studies' hypothesis that the photo-thermal interaction is key in the NIR laser effect. 15,16,25,27,44,45,53 We selectively excluded one channel from the temperature dependency at a time in the CGC-model, which cannot be performed experimentally. We found I D and I NaP channels to be critical for the activity modulation, radically changing the waveform when altering temperature dependency.…”

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

“…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].…”

“…INS has been achieved with pulse durations in the range of microseconds [10], milliseconds [11], and seconds [8]. Moreover, the accumulation of heat caused by a sequence of light pulses at a repetition rate higher than 3 Hz could result in nerve responses of greater amplitude [12], [13]. However, former studies did not report an impact of the stimulation rate on the recorded compound action potential amplitude [7], [14].…”