Infrared light excites cells by changing their electrical capacitance

TLDR

Optical stimulation, especially pulsed infrared lasers >1.5 µm, has enabled advances in neuroscience and medicine, yet the biophysical mechanism underlying its ability to directly activate nerves and muscles remains unclear. The authors aim to demonstrate that infrared light excites cells through a novel, highly general electrostatic mechanism. Infrared pulses are absorbed by water, causing rapid local heating that reversibly alters the plasma membrane’s electrical capacitance and depolarizes the target cell. The study shows that this capacitance‑based depolarization is fully reversible, depends only on basic membrane properties, and highlights the generality and medical potential of pulsed infrared stimulation.

Abstract

Optical stimulation has enabled important advances in the study of brain function and other biological processes, and holds promise for medical applications ranging from hearing restoration to cardiac pace making. In particular, pulsed laser stimulation using infrared wavelengths >1.5 μm has therapeutic potential based on its ability to directly stimulate nerves and muscles without any genetic or chemical pre-treatment. However, the mechanism of infrared stimulation has been a mystery, hindering its path to the clinic. Here we show that infrared light excites cells through a novel, highly general electrostatic mechanism. Infrared pulses are absorbed by water, producing a rapid local increase in temperature. This heating reversibly alters the electrical capacitance of the plasma membrane, depolarizing the target cell. This mechanism is fully reversible and requires only the most basic properties of cell membranes. Our findings underscore the generality of pulsed infrared stimulation and its medical potential. Pulsed infrared laser light can directly stimulate nerves and muscles, but the underlying biophysical mechanism has remained enigmatic. This study reveals that infrared pulses depolarize target cells by reversibly altering the electrical capacitance of the plasma membrane.