Post-traumatic stress disorder (PTSD) is a mental disease that may occur in people who have experienced or witnessed traumatic events, such as wars and natural disasters. It can occur in all people. Approximately 7% of American adults currently have PTSD [1]. Certain population, such as veterans, are at a high-risk of developing PTSD. For instance, up to 30% of Vietnam War veterans have been diagnosed with PTSD, and 15% still experience symptoms after 15 years since the war. During the COVID-19 epidemic in 2020, a survey of 205 nursing staff in Wuhan showed that the positive rate of PTSD was as high as 50.73%. The symptoms of PTSD include avoidance, intrusive symptoms and flashbacks, mood and cognitive disruptions, and hyperarousal/reactivity symptoms, which can lead to depression, alcohol and substance abuse, social phobia, and even suicide of patients [2, 3].

Recently, physical therapy (sound, light, electricity, magnetism) as a non-invasive treatment strategy for nervous system diseases receives more and more attention. Light has been used to treat diseases for more than three thousand years. Update to the end of 19th century, the phototherapy was successfully applied to treat psoriasis, rickets, vitiligo, smallpox and cutaneous tuberculosis. Over the past two decades, transcranial phototherapy emerged as a promising non-invasive treatment option for various brain disorders, such as stroke, traumatic brain injury (TBI), Alzheimer’s disease (AD), Parkinson’s disease, and psychiatric disorders [4, 5].

Luckly, the symptoms of PTSD patients will appear in one month of traumatic event exposure, which provides an opportunity for early intervention. In the present work, we explored the preventive effect of pulsed transcranial irradiation on PTSD in animal experiments. The rats received 10 Hz pulsed 810 nm laser-phototherapy in 30 min of traumatic event exposure. Surprisingly, a single dose of 10 Hz pulsed 810 nm laser-phototherapy (P-PT) completely prevented the occurrence of PTSD like comorbidities in rats. We also compared the effects of P-PT and continuous wave 810 nm laser-phototherapy (CW-PT) in preventing PTSD-like comorbidities in rats. The results revealed that P-PT was effective in preventing both freezing and anxiety behavior in stressed rats. However, CW-PT only had a preventive effect on freezing behavior but not anxiety.

The mechanism of phototherapy is widely considered to be providing the energy for the injured or dysfunctional cells. In our study, we observed that pulsed 810 nm laser (10 Hz) was more effective in preventing PTSD-like comorbidities in rats than CW-PT under the same dose of irradiation. These results suggest that the preventive effect on PTSD of P-PT may not be solely attributed to energy, but also to other yet unknown benefits. Previous study reported that the PTSD rats showed a significant decrease in delta and theta power spectra of the electroencephalogram. The theta frequency band activity was decreased in both resting and working condition in people with PTSD compared to control subjects [6, 7]. So, we supposed that resonance may occur between the frequency of the pulsed light and that of the brain waves, particularly in the hippocampal region, where all mammals exhibit prominent theta wave oscillation.

Importantly, based on our found, we have already designed the wearable equipment and applied the patent. The clinical trial to determine if this treatment strategy plays a role in prevention of PTSD in human has been applied.

In summary, this work found that a single dose of 10 Hz pulsed red light can prevent the occurrence of PTSD like comorbidities in rats. It has the potential to be a non-invasive early intervention for preventing the occurrence of PTSD-like comorbidities in humans.

References

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