A new study has found that light therapy applied to mice during deep sleep increased the brain’s ability to clear away beta-amyloid, a toxic protein linked to the development of Alzheimer’s disease. The finding may lead to a non-drug, non-invasive treatment for the condition.

Despite their tireless efforts, researchers have been unable to develop a safe and effective way of treating Alzheimer’s disease (AD) using pharmaceuticals, which has meant turning to non-pharmaceutical methods. A new study has demonstrated the therapeutic potential of light therapy, or phototherapy, in treating AD, showing promising results in mice that the researchers hope can be just as effective in humans.

In the study, the researchers used photobiomodulation (PBM), a non-pharmaceutical therapy that employs red and near-infrared lights to stimulate the body to heal itself. There’s evidence to suggest that PBM causes an increase in metabolism and microcirculation in the brain, in addition to reversing oxidative stress and inflammation. Recent studies discovered that PBM can stimulate the brain’s lymphatic system to remove wastes and toxins.

There is a lymphatic vascular system in the meninges, the membrane that covers and protects the brain and spinal cord. These meningeal lymphatic vessels, or MLVs, have been shown to clear away beta-amyloid, which has long been linked to Alzheimer’s disease. It’s thought abnormal levels of this naturally occurring protein clump together to form plaques between neurons, disrupting cell function.

Because the brain’s lymphatic system has been found to be activated during sleep, the researchers tested the effect of PBM during wakefulness and non-REM (deep) sleep. They injected beta-amyloid into the hippocampus – the area of the brain concerned with memory and learning – of mice after destroying their MLVs using a laser. PBM was applied to the mice once a day for seven days using an LED.

Measuring the level of beta-amyloid in the hippocampus following PBM, the researchers found that levels were lower whether it was applied during wakefulness or sleep but that PBM during sleep produced a greater reduction in beta-amyloid. They concluded that PBM stimulated the evacuation of beta-amyloid from the hippocampus more effectively during sleep than wakefulness.

The researchers also observed that despite the destruction of the MLVs, which had suppressed their ability to remove beta-amyloid, that ability was restored following treatment and was more effective when PBM was applied during sleep than during wakefulness.

“In our results, we discovered that PBM promotes restoration of lymphatic functions after injury of MLVs that is more effective if PBM is used during deep sleep vs. wakefulness,” said the researchers.

They say that this non-pharmaceutical, non-invasive treatment could be used in people with AD and other conditions that involve the brain’s lymphatic system.

“Since pharmacological therapy of AD have failed to show effectiveness or safety, PBM as a non-invasive and safe approach has the high prospects for implementation in clinical practice for the treatment of brain diseases with lymphatic disorders, such as AD, Parkinson’s disease, glioma, traumatic brain injury, intracranial hemorrhages,” the researchers said.

The study was published in the journal Frontiers of Optoelectronics.