Boosted Immune Cells Clear Brain Plaques
Just like a strobe, our brains flicker, generating electrical impulses at different frequencies. Gamma oscillations range from 25 to 80 hertz (cycles per second) and are believed to have roles in memory, attention and perception. People with Alzheimer's disease are known to have impaired function in the gamma range. In 2016, neuroscientist Li-Huei Tsai and her research group at MIT tested what would happen if white light were flashed at mice for an hour at a frequency of 40 Hertz (40 times a second). These mice were specially engineered to develop Alzheimer's-type symptoms, so the plaques (amyloid) and tangles (tau) typically seen in the disease had built up in their brains, and they exhibited irregular brain activity in the gamma range. The result of the experiment was that a steady frequency of 40 Hertz was reflected back from the mice in the visual cortex, the area that receives and processes visual information -- a not unexpected result. But something else happened that the scientists were unprepared for. The microglia in the visual cortex were strongly stimulated. These are immune cells that clear debris and toxic waste from the brain. This light stimulation caused a sizable reduction of amyloid and tau. Dr Tsai described the effect as "most remarkable."Better Cognitive Function
For their latest study, published in the journal Cell in March, instead of light, they tested the effect of sound. Listening to 40 clicking sounds a second, one hour a day for seven days, the mice not only experienced a large reduction of amyloid and tau in the auditory cortex, where sound is processed, but likewise in an area located nearby - the hippocampus - a key part of the brain for learning and memory. Compared to mice that didn't receive the stimulation, they performed much better on tests of navigation round a maze, where landmarks must be recalled, and the recognition of objects they'd previously been shown. As in the light test, the microglia were stimulated, but in addition, there were positive changes in the brain's blood vessels. The final experiment was to see the effect of combining both light and sound. The microglia response was far stronger, and amyloid plaques were reduced not only by a huge amount, but also in a much larger area of the brain. This included the prefrontal cortex where higher cognitive processes take place. The treated mice performed far better on a set of cognitive tests. For instance, untreated mice shown an object they’d seen before reacted as though they'd never seen it. The stimulated mice spent far less time examining it because they recognized the object. Overall, the result of combing light and sound was greater than either one alone."Unbelievable"
Commenting on the findings, Dr Tsai said, "It was unbelievable. This is the first time we've seen that this non-invasive stimulation can improve cognitive function. It's not a drug or an antibody or anything, it's just light and sound." Shannon Macauley, a neuroscientist at Wake Forest School of Medicine, who was not involved with the study, enthused, "I think it’s an absolutely fascinating paper." The fact that amyloid and tau fell in both the hippocampus and prefrontal cortex is, she explained, "one of the big jumps in the new paper. "These are the learning and memory centers of the brain. And there was about a 40 or 50 percent decrease in amyloid and tau levels. It’s an absolutely impressive feat." Although the effects fade over time, it would be simple to apply regularly at home by patients, if they’re able, or by a relative or caregiver. The light-sound therapy has already been tested for safety on healthy volunteers, and early-stage Alzheimer's patients are currently being recruited for the first human trial.