Oscillating Light Therapy Could Help Treat Alzheimer's

Using optogenetics, the researchers induced gamma oscillations at 40 hertz in the hippocampus. After an hour of stimulation at 40 hertz, the researchers found that hippocampal levels of amyloid-β (Aβ) proteins fell by 40-50%; this effect was not observed at other frequencies.

The researchers then built a device comprised of a strip of light emitting diodes (LEDs) capable of being programmed to flicker at different frequencies and induce gamma oscillations in the brain when shone in the eyes. The flickering effect stimulates interneurons, cells that synchronize the gamma activity among brain cells to help them communicate with each other. The found, similarly, that one hour of exposure to the light flickering at 40 hertz set up gamma oscillations and halved Aβ levels in the visual cortex of mice in the early stages of AD; but the Aβ proteins returned to previous levels within 24 hours.

In further tests with longer exposure on mice in more advanced stages of Ad, the researchers found markedly reduced Aβ levels and plaque deposits. They also found that the gamma oscillations reduced another hallmark of AD, abnormal tau proteins that form tangles in the brain. Finally, the researchers also showed that gamma oscillations caused the induction of genes associated with morphological transformation of microglia, with histological analysis confirming increased microglia co-localization with Aβ. The study was published on December 7, 2016, in Nature.

“More research needs to be done before we can say if the therapy works for human patients with Alzheimer's disease,” said senior author professor Li-Huei Tsai, PhD, of MIT. “It's a big 'if',' because so many things have been shown to work in mice, only to fail in humans. But if humans behave similarly to mice in response to this treatment, I would say the potential is just enormous, because it's so noninvasive, and it's so accessible.”

Networks of neurons in the brain fire in a coordinated fashion, generating rhythmic waves of electric activity that occur at different frequencies. In the 20-50 Hz range, gamma oscillations are involved in memory encoding and retrieval, perception, and attention. Animal studies show that they serve to synchronize intercolumnar input in the cat visual cortex. Other studies in experimental animals also pointed to the role of gamma oscillations in spatial and working memory. Changes in these brain waves have been seen in several brain disorders, including in patients with AD.

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