Photobiomodulation and the brain – has the light dawned?

tumour. However, he was surprised to observe in treated animals that the incisions made to implant the tumour healed faster than the controls, and the shaved hair also grew back faster. Mester called this phenomenon ‘laser biostimulation’ and it later became known as ‘low-level laser therapy’, or LLLT 1. The mechanism of action of PBMT has been under intense investigation ever since it was discovered, but in recent years there has been some consensus among experts on this thorny topic2. The principal chromophore (light-absorbing molecule) has been identified as cytochrome c oxidase (CCO), which is unit IV of the mitochondrial respiratory chain and responsible for reducing oxygen to water with the simultaneous production of protons that are used to drive the synthesis of adenosine triphosphate (ATP), i.e. the cellular energy source. The fact that CCO absorbs light in the red region of the visible spectrum (600–690 nm) and in the NIR (760–940 nm), which are the most clinically effective wavelengths, bolsters this hypothesis. One of the most general observations made in PBMT is an increase in ATP in cells and tissues. Recently, it has become likely that there is a second chromophore that absorbs longer wavelengths (980 nm and 1064 nm), and this has been tentatively identified as water (possibly in the form of nanostructured water which is a thin layer that forms on biological membranes). This may be particularly important in activating transient receptor potential (TRP) ion channels. The mechanism of PBM absorption by chromophores is shown in Figure 1. Photobiomodulation therapy