Animal study tests novel way to influence Alzheimer's-related brain changes

Gamma brain waves—electrical charges that help link and process information from all parts of the brain—are known to slow down in the brains of people with Alzheimer's disease and other neurological or psychiatric disorders. NIH-funded researchers wanted to better understand the relationship between changes in gamma rhythms and Alzheimer's-related cellular changes.

They discovered that exposing an Alzheimer's mouse model to flickering LED lights could stimulate gamma waves, which not only reduced levels of beta-amyloid plaques in the brain—a hallmark of the Alzheimer's—but boosted the clearance of harmful debris by microglia cells. This finding, published online Dec. 7 in Nature, provides new insight about a possible noninvasive approach to treating Alzheimer's disease.

The findings from a research team led by Dr. Li-Huei Tsai at the Massachusetts Institute of Technology, Cambridge, are preliminary but highlight the promise of optogenetics, a biological technique that uses light to control and monitor the activities of neurons that have been genetically modified to be extra-sensitive to light in animal models.

Using a strip of LED lights that flickered at different speeds, the researchers found that a single, hour-long treatment of light flashing at 40 hertz increased gamma waves and reduced beta-amyloid levels by half in the visual cortex of mice in the very early stages of Alzheimer's. Within 24 hours, however, amyloid levels returned to normal in this brain region, which processes information from the eyes. When the scientists exposed mice with even higher levels of amyloid buildup to 1 hour of flickering light per day over 7 days, the number of amyloid plaques and levels of free-floating amyloid decreased. The treatment also ramped up the efficiency of microglia, reducing the number of amyloid plaques and free-floating amyloid.

More research in animal models is needed to determine how long these effects last, but the proof-of-concept findings will inform the understanding of the various factors involved in Alzheimer's disease onset and progression.

Reference: Iaccarino, H.F., et al. Gamma frequency entrainment attenuates amyloid load and modifies microglia. Nature. 2016 Dec 7;540(632):230-235.