Transcranial photobiomodulation influences BOLD responses during finger sequence execution: An fMRI Study in young and older adults

Transcranial photobiomodulation (PBM) is an emerging non-invasive brain stimulation method that is thought to increase neural metabolism by stimulating ATP production by the mitochondria. However, the mechanisms of action and the effects on the human brain are still unclear. In the present study, we investigated the potential of this method to enhance Blood Oxygen Level Dependent (BOLD) responses during the execution of a motor task in young and aged participants. Sixty young and aged participants were included in this single-blinded, sham-controlled, randomised, crossover study. They underwent an fMRI recording before and after 24-min stimulation with a 80-LEDs helmet emitting transcranially red and near infrared light. Post vs Pre BOLD signal was compared between PBM and SHAM, in each group. At baseline, aged participants showed reduced BOLD signal compared to young ones, in key regions of the sensorimotor processing, principally the left primary motor cortex and striatum. Transcranial PBM did not have a real impact in the young group. In aged participants, analysis performed on the whole brain did not reveal widespread changes, but rather local increases in BOLD responses in the right ventral premotor cortex and insula. More specifically, a regional analysis further showed increased BOLD responses in the left primary motor cortex, and right dorsal and ventral premotor regions and striatum. Some of these regions were under-activated at baseline in aged participants relatively to the young ones. These results suggest that transcranial PBM can increase fMRI BOLD responses locally in some task-related regions, particularly in aged subjects. Further research are needed to distinguish neural from vascular effects in transcranial PBM.