At left, the mouse cortex shows a reduction in amyloid plaques following visual and auditory stimulation, compared to the untreated mouse at right.Image Credit: Gabrielle Drummond / MIT
Massachusetts Institute of Technology researchers are using a unique combination of light and sound to improve cognitive and memory impairments similar to those seen in Alzheimer's patients. The noninvasive treatment works by inducing brain waves known as gamma oscillations and so far the team has only performed the treatment on mice.
“When we combine visual and auditory stimulation for a week, we see the engagement of the prefrontal cortex and a very dramatic reduction of amyloid,” said Li-Huei Tsai, director of MIT’s Picower Institute for Learning and Memory and the senior author of the study.
The MIT researchers have already performed some preliminary safety tests of this type of stimulation in healthy human subjects, but Tsai said more work will be needed to find out if the treatment will work for human patients.
The study was published in the March 14 issue of Cell.
Previous studies have suggested that Alzheimer’s patients have impairments of their gamma-frequency oscillations, which range from 25 to 80 hertz (cycles per second) and are believed to contribute to brain functions such as attention, perception, and memory.
In 2016, Tsai and her colleagues first reported the beneficial effects of restoring gamma oscillations in the brains of mice that are genetically predisposed to develop Alzheimer’s symptoms. In that study, the team used light flickering at 40 hertz, delivered for one hour a day. They found that this treatment reduced levels of beta amyloid plaques and another Alzheimer’s-related pathogenic marker, phosphorylated tau protein. The treatment also stimulated the activity of debris-clearing immune cells known as microglia.
In that study, the improvements generated by flickering light were limited to the visual cortex. In their new study, the researchers set out to explore whether they could reach other brain regions, such as those needed for learning and memory, using sound stimuli. They found that exposure to one hour of 40-hertz tones per day, for seven days, dramatically reduced the amount of beta amyloid in the auditory cortex (which processes sound) as well as the hippocampus, a key memory site that is located near the auditory cortex.
“What we have demonstrated here is that we can use a totally different sensory modality to induce gamma oscillations in the brain. And secondly, this auditory-stimulation-induced gamma can reduce amyloid and Tau pathology in not just the sensory cortex but also in the hippocampus,” Tsai said.
Tsai is a founding member of MIT’s Aging Brain Initiative.
The researchers also tested the effect of auditory stimulation on the mice’s cognitive abilities. They found that after one week of treatment, the mice performed much better when navigating a maze requiring them to remember key landmarks. They were also better able to recognize objects they had previously encountered.
They also found that auditory treatment induced changes in not only microglia, but also the blood vessels, possibly facilitating the clearance of amyloid.