Optical methods of neural stimulation are seeing steadily increasing use in neuroscience and neural engineering. Amongst the optical methods, infrared neural stimulation (INS) has been demonstrated in a wide range of peripheral and central neural tissue, predominantly in the context of bionic devices. INS uses pulsed laser light at infrared wavelengths (typically between 1400 nm and 2100 nm) to generate stimuli in neural tissue. It shares many of the advantages of other optical techniques (e.g. optogenetics and glutamate uncaging), such as a high degree of spatial selectivity and non-contact stimulation. Furthermore, in its most basic implementation INS requires no modification of the target tissue, although there is potential to improve the process by adding absorbing particles to the tissue.
In order to maximise the effectiveness of INS, it is important that the mechanisms by which it operates are understood. Previous work has shown that INS is mediated by rapid heating due to absorption of the incident light by water molecules in the tissue. This rapid heating causes transient changes in membrane capacitance1 , and can also directly activate temperature sensitive (TRPV) ion channels in cells that express them2 . An additional effect that may occur but that has not been previously shown in relation to INS, is that heating can lead to changes in membrane permeability3 .
We present the findings of patch clamp recordings from cultured primary auditory neurons exposed to pulsed infrared light (1870 nm). Our results are largely consistent with previous in vitro measurements of other cell types1. However, we also see some evidence of temperature mediated changes in membrane permeability. This effect could constitute an additional, highly general mechanism of INS that has not previously been reported.