Effectiveness of Light for Enhancement of Cognition by Transcranial Repeated Application (ELECTRA)

Photobiomodulation (PBM), also called low-level light therapy (LLLT), uses optical power densities less than 100 mW/cm², and usually in the red (600-700 nm) or near infrared (NIR) 780-1000 nm wavelength range. Different light sources (coherent lasers or non-coherent LEDs) used for PBM have been shown to produce beneficial cellular effects and to be responsible for preservation and recovery of tissue function in controlled trials in a wide range of disorders typified by stress injury or degeneration. During PBM, absorption of red or near-infrared photons by cytochrome c oxidase in the mitochondrial respiratory chain causes an increase in cellular respiration that continues for much longer than the light is present when delivered at appropriate fluence and exposure durations. Primary cellular effects include increases in mitochondrial activity and ATP levels, production of low levels of reactive oxygen species, induction of transcription factors (including the pro- survival NF-kB), and inhibition of apoptosis. Over the past decade several studies have reported that a single, transcranial PBM treatment at 810 nm delivered to the head had significant, beneficial effect when used to treat acute ischemic stroke in several different animal models and also in human clinical trials. A similar approach was used to treat acute traumatic brain injury (TBI) in mice and in humans. Pathological examination of the mouse brains demonstrated up- regulation of brain-derived neurotrophic factor (BDNF) and stimulated neurogenesis in the hippocampus and increased synaptogenesis in the cortex. A clinical trial is currently in progress at MGH to treat persons with acute moderate TBI. Several studies have shown improvement of cognitive function in persons with chronic TBI. Studies have also been conducted in animal models and in persons with Alzheimer's disease, Parkinson's disease, depression and anxiety. Only a very limited number of studies have so far been carried out to test NIR photobiomodulation in normal experimental rodents and in normal human volunteers. In this study, an LED array light source will be used that has been cleared by the FDA for other human uses.