The Effect of Photobiomodulation on Heart Rate Variability in Healthy Adults Subjected to the Maastricht Acute Stress Test (MAST): A Sham-controlled, Within-subject Study

Photobiomodulation (PBM) is a non-invasive therapeutic technique that uses low-level light, typically in the red or near-infrared spectrum, to stimulate biological tissues. This approach has been increasingly studied for its beneficial effects on wound healing, mood, and sleep quality. Recent research has also highlighted PBM's potential in enhancing brain function, neuroplasticity, and cognitive performance. For example, prior studies have demonstrated that transcranial PBM (i.e., PBM delivered to the head) can help modulate neuronal activity, improve cerebral blood flow, and promote neuroprotective effects for traumatic brain injury and stroke. Given these findings, PBM may also have potential for influencing autonomic function and stress physiology. However, to date, little is known about the effects of PBM on the autonomic nervous system, particularly its influence on vagal activity and heart rate variability (HRV).

This study aims to fill this gap by investigating the effects of transcutaneous cervical plus intranasal PBM on HRV in healthy individuals subjected to experimental stress. Specifically, the Maastricht Acute Stress Test (MAST) will be used, which is a validated stress protocol that has been shown to strongly and reliably induce acute autonomic stress responses. A within-subject design will be employed with four repeated visits per participant to examine the effects of both PBM and sham intervention applied before and after stress induction on vagal activity, as measured by HRV. As the first study to examine PBM's impact on HRV, this research will provide valuable insights into the potential of PBM as a novel, non-invasive approach to modulating autonomic regulation, particularly in the context of stress.