Pulsed infrared (IR) light has been used in multiple animal models to inhibit neural activity. Duke et al.
reported inhibition associated with a temperature increase of ~8°C in Aplysia californica buccal nerve 2
(BN2). There is no evidence that the current irradiation schemes alters nerve functionality, however lower
temperatures provide a safer environment for sustained inhibition. Inhibition paradigms use a single optical
fiber to deliver IR light, resulting in a single hotspot within the nerve. One proposed method for decreasing
peak temperatures is to use a lower radiant exposure over a greater area, effectively heating the nerve more
evenly. Preliminary computational modeling suggests that using two axially adjacent optical fibers reduces
peak temperatures required for infrared neural inhibition (INI). This hypothesis is being validated in vitro in
Aplysia. Pleural abdominal nerves were dissected out, and suction electrodes were applied to electrically
stimulate and record neural activity. A custom probe (core diameters= 400 μm) was used to simultaneously
apply IR light from two diode lasers (Lockheed-Martin, λ=1875nm) to the nerve and monitor the radiant
exposure out of each. Radiant exposures required for inhibition using a single fiber were reduced by ~37.4%
by using two axially adjacent optical fibers. While mechanisms behind infrared inhibition are not fully
understood, data suggests that a threshold temperature is required. By reducing peak temperatures, neural
block using IR light will subject nerves to lower peak temperatures and provide a more research and clinically
Jeremy B. Ford, Michael W. Jenkins, Hillel J. Chiel, and E. Duco Jansen, "Reducing peak temperatures during infrared inhibition of neural potentials," Proc. SPIE 10052, Optogenetics and Optical Manipulation, 100520B (Presented at SPIE BiOS: January 28, 2017; Published: 28 February 2017); https://doi.org/10.1117/12.2250019.
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