Transcranial laser stimulation: Mitochondrial and cerebrovascular effects in younger and older healthy adults

Background: Transcranial laser stimulation is a novel method of noninvasive brain stimulation found safe and effective for improving prefrontal cortex neurocognitive functions in healthy young adults. This method is different from electric and magnetic stimulation because it causes the photonic oxidation of cytochrome-c-oxidase, the rate-limiting enzyme for oxygen consumption and the major intracellular acceptor of photons from near-infrared light. This photobiomodulation effect promotes mitochondrial respiration, cerebrovascular oxygenation and neurocognitive function. Pilot studies suggest that trans cranial photobiomodulation may also induce beneficial effects in aging individuals. Objectives: Randomized, sham-controlled study to test photobiomodulation effects caused by laser stimulation on cytochrome-c-oxidase oxidation and hemoglobin oxygenation in the prefrontal cortex of 68 healthy younger and older adults, ages 18-85. Methods: Broadband near-infrared spectroscopy was used for the noninvasive quantification of bilateral cortical changes in oxidized cytochrome-c-oxidase and hemoglobin oxygenation before, during and after 1064-nm wavelength laser (IR-A laser, area: 13.6 cm(2), power density: 250 mW/cm(2)) or sham stimulation of the right anterior prefrontal cortex (Brodmann Area 10). Results: As compared to sham control, there was a significant laser-induced increase in oxidized cytochrome-c-oxidase during laser stimulation, followed by a significant post-stimulation increase in oxygenated hemoglobin and a decrease in deoxygenated hemoglobin. Furthermore, there was a greater laser-induced effect on cytochrome-c-oxidase with increasing age, while laser-induced effects on cerebral hemodynamics decreased with increasing age. No adverse laser effects were found. Conclusion: The findings support the use of transcranial photobiomodulation for cerebral oxygenation and alleviation of age-related decline in mitochondrial respiration. They justify further research on its therapeutic potential in neurologic and psychiatric diseases. (C) 2021 The Author(s). Published by Elsevier Inc.

Automated summary

Transcranial laser stimulation is a safe and effective method for improving prefrontal cortex neurocognitive functions, promoting mitochondrial respiration and cerebrovascular oxygenation. Laser-induced effects on cytochrome-c-oxidase increased with age, while effects on cerebral hemodynamics decreased. Further research on the therapeutic potential in neurologic and psychiatric diseases is warranted.