Recent advances in low-level laser therapy on depression

Photobiomodulation (PBM), as a form of light therapy, has been applied broadly in the medical practice. The biological photoreceptors use small-molecule cofactors called chromophores to detect light and convert a physical signal into a biochemical signal transmission cascade. Visible light (380–780 nm) can activate specialized photoreceptors to stimulate vision and regulate circadian rhythm. Compared with visible light, near-infrared (NIR) light (780–1,100 nm) has better tissue penetration depths, enabling us to carry out non-invasive low-level laser therapy (LLLT) for different tissues. Mitochondrial cytochrome c oxidase is the main NIR photoreceptor. The basic effect is to promote the generation of ATP through the respiratory chain. LLLT can enhance blood circulation, alleviate inflammation, promote muscle damage repair, stem cell proliferation and so on. The neuroprotective effect of LLLT on central nervous system (CNS) diseases has been preliminarily verified in animal models, which is expected to improve the cognitive function of Alzheimer’s patients, motor symptoms of Parkinson’s patients and mental disorders of patients with depression, thus improving the quality of life of patients. Understanding its protective effect and mechanisms will contribute to better therapeutic application in the future. In this review, we will discuss the antidepressant effect of LLLT, its possible mechanisms, and existing problems with its applications.