Optically mediated nerve stimulation: Identification of injury thresholds.
OBJECTIVE
Transient optical nerve stimulation is a promising new non-contact, spatially precise, artifact-free neural excitation technique useful in research and clinical settings. This study evaluates safety of this pulsed infrared laser technique by histopathologic examination of stimulated peripheral nerves.


METHODS
Exposed rat sciatic nerves were functionally stimulated with the pulsed Holmium:YAG laser, previously validated as an effective tool for optical stimulation. Nerves were removed immediately and up to 2 weeks after stimulation and assessed histologically for thermal damage. Laser parameters studied include upper limits for radiant exposure, repetition rate, and duration of stimulation.


RESULTS
Radiant exposures with <1% probability of thermal tissue damage (0.66-0.70 J/cm(2)) are significantly greater than radiant exposures required for reliable stimulation (0.34-0.48 J/cm(2)). The upper limit for safe laser stimulation repetition rate occurs near 5 Hz. Maximum duration for constant low repetition rate stimulation (2 Hz) is approximately 4 minutes with adequate tissue hydration.


CONCLUSIONS
Results confirm that optical stimulation has the potential to become a powerful non-contact clinical and research tool for brief nerve stimulation with low risk of nerve thermal damage.
Department of Biomedical Engineering, Vanderbilt University, Box 351631 Station B, Nashville, Tennessee 37235, USA.
Jonathon D
JD
Wells
Sharon
S
Thomsen
Peter
P
Whitaker
E Duco
ED
Jansen
Chris C
CC
Kao
Peter E
PE
Konrad
Anita
A
Mahadevan-Jansen
D000200:Action Potentials; D000818:Animals; D005260:Female; D028022:Low-Level Light Therapy / Q000009:adverse effects / Q000379:methods*; D008297:Male; D023421:Models, Animal; D051381:Rats; D017207:Rats, Sprague-Dawley; D012584:Sciatic Nerve / Q000293:injuries / Q000473:pathology* / Q000502:physiology / Q000528:radiation effects*