Differences in conduction velocities of nerve fibers excited by infrared and electrical stimulation

Infrared neural stimulation (INS) uses short optical pulses to activate nerves. While electrical stimulation (ES) activates large-diameter fibers first, light may preferentially activate small-diameter fibers first, which could be valuable for many clinical applications.

This study used a compact diode laser of 1470 nm to perform INS. Conduction velocity (CV) measurements were performed to assess differences in fiber type activation between INS and ES in the rat sciatic nerve and the goat vagus nerve. The rat sciatic nerve was chosen as a standard model because of its well-characterized physiology and extensive use in studies of INS mechanisms. The goat vagus nerve was chosen because of its expected high proportion of small-diameter fibers and its larger size, which allows sufficient separation between recording units to optimize CNAP measurements.

The results showed that in the rat sciatic nerve, ES-excited fibers had significantly higher CVs (9.81 ± 3.18 m/s) than INS-excited fibers (8.10 ± 2.82 m/s). In the goat vagus nerve, ES produced a mean CV of 6.47 ± 1.25 m/s, but INS did not produce clearly distinguishable compound nerve action potential, highlighting the challenges of applying INS to larger nerves.

To the best of our knowledge, CV is, for the first time, measured to identify the type of nerve fiber excited by INS.

These results suggest that INS may preferentially activate smaller diameter fibers, providing insight for potential neuromodulation applications.