Abstract
The non-invasive delivery of laser light to the brain, termed transcranial photobiomodulation (tPBM), has been shown to stimulate vascular and metabolic function in the rodent brain. Given the large number of neurological disorders marked by impaired blood flow and metabolism, it is important to objectively evaluate the reported effects in humans. To date, however, neurophysiological evidence of tPBM effects in the human brain is scarce. Here we combined tPBM with functional magnetic resonance imaging (fMRI) by recording the blood-oxygenation-level dependent (BOLD) signal before, during, and after application of tPBM to the right forehead of 20 healthy participants. We found both acute and outlasting BOLD increases as high as 31% in regions of the prefrontal cortex within 30 mm of the site of light incidence. The observed effect was consistent with rapid inflow of blood to the stimulated brain region, coupled with an increase in oxidative metabolism. Our findings underscore the therapeutic potential of tPBM in the human brain.