Mechanisms of photobiomodulation in the brain

This chapter discusses the mechanisms of action of photobiomodulation (PBM) in the brain. The primary molecular chromophores including cytochrome c oxidase in the mitochondrial respiratory chain, light-sensitive ion channels, and exclusion zone nanostructured water are covered. The secondary processes of PBM are addressed as they particularly affect the brain. Metabolism is increased due to the stimulation of mitochondria with more adenosine triphosphate to fuel the brain processes. Blood flow and cerebral oxygenation are also increased. Neuroprotection is another beneficial feature of PBM, particularly as it limits brain damage after stroke or traumatic brain injury. Oxidative stress is limited by induction of antioxidant defenses. The antiinflammatory effects of PBM are evidenced by a switch of the microglial phenotype from M1 to M2 possible mediated by an increase in oxidative phosphorylation. Neurogenesis (formation of new brain cells) and synaptogenesis (formation of new connections between existing brain cells) are stimulated and possibly mediated by the increase in neurotrophins. Stem cells are activated and systemic effects possibly mediated by blood irradiation are covered.