Photobiomodulation Helmet

Photobiomodulation describes the use of red or near-infrared light to stimulate, heal, regenerate, and protect tissue that has been injured, is degenerating, or is at risk of dying. ^[1] In transcranial PBM, near-infrared light is often applied to the forehead because of better penetration, and inexpensive LED arrays have enabled light-emitting helmets or 'brain caps'. ^[1] Transcranial photobiomodulation is the process of delivering light photons through the skull to benefit from its modifying effect on brain tissue. ^[2]

The mechanism involves activation of cytochrome c oxidase in the mitochondrial respiratory chain, enhancing ATP synthesis and triggering anti-oxidant, anti-inflammatory, and anti-apoptotic responses that foster neurogenesis and synaptogenesis. ^[3] In humans, PBM applied to the head has been shown to increase regional cerebral blood flow and tissue oxygenation and to modulate activation in intrinsic brain networks. ^[4] A challenge for the approach is that transcranial delivery is limited by light's poor penetration into tissue, prompting exploration of alternative delivery methods. ^[3] Both focal and global helmet-style stimulation appear to act at the vascular level by increasing regional cerebral blood flow and at the neural level by changing neuronal activity. ^[5]

A systematic review of human studies found that 29 of 35 studies reported positive improvement in cognitive functions after transcranial PBM, including all nine studies in subjective memory complaints, mild cognitive impairment, and dementia. ^[6] However, the authors caution that only half of the reviewed clinical trials were randomized controlled trials, so further investigation is warranted. ^[6] An umbrella review of meta-analyses of randomized trials found moderate-certainty evidence that PBM improves cognitive function, with an equivalent standardized mean difference of 0.49. ^[7] In Alzheimer's and Parkinson's disease, clinical studies demonstrate brain PBM safety with particularly promising results in Alzheimer's, but their exploratory design and inconsistent quality yield a low level of evidence that does not currently support widespread clinical use. ^[8] A meta-analysis of transcranial PBM for depression provided only weak support, since the few double-blind sham-controlled studies did not show statistically significant superiority over sham. ^[9]

Among non-pharmacological interventions studied for age-related neurocognitive impairment, PBM has gained prominence and can improve attention, learning, memory, and mood in older people. ^[10] A 2023 National Institute on Aging workshop concluded that PBM holds potential as a safe, inexpensive therapeutic approach for a range of age-related diseases and cognitive decline, while noting that more research is needed to optimize protocols. ^[11] A major barrier to adoption is the lack of standardized protocols, with a wide variety of parameters used for the same conditions and a need for sham-controlled comparative studies. ^[12]