Exploring the Effects of Near Infrared Light on Resting and Evoked Brain Activity in Humans Using Magnetic Resonance Imaging

Abstract

We explore whether near infrared light can change patterns of resting (task-negative) and/or evoked (task-positive; eg finger-tapping) brain activity in normal, young human subjects using fMRI (functional magnetic resonance imaging). To this end, we used a vielight transcranial device (810 nm) and compared the scans in subjects after active- and sham-light sessions. Our fMRI results showed that, while light had no effect on cerebral blood flow and global resting state brain activity (task-negative), there were clear differences between the active- and sham-light sessions in the patterns of evoked brain activity after finger-tapping (task-positive). The evoked brain regions included the putamen, primary somatosensory and parietal association cortex, and the overall effect of the light was to suppress or reduce their activity. We also found that while light had no effect on the resting functional connectivity of the putamen and primary somatosensory cortex and the rest of the brain, it did have an effect on the functional connectivity of parietal association cortex. In summary, our fMRI findings indicated that transcranially applied light did have a major impact on brain activity in normal subjects, but only when the brain region was itself functionally active, when undertaking a particular task. We suggest that these light-induced changes, particularly those in parietal association cortex, were associated with attention and novelty, and served to deactivate the so-called default mode network. Our results lay the template for our planned fMRI explorations into the effects of light in both Alzheimer's and Parkinson's disease patients.