A study in mice by researchers at MIT has found exposure to flickering light stimulated brain waves appears to prompt the brain’s immune cells to absorb the sticky amyloid proteins that are the most visible hallmarks of Alzheimer’s disease (The Guardian, 2016).

The authors of the study don’t yet know whether the findings would be replicated in humans or whether cognitive deficits as well as the visible symptoms of Alzheimer’s would be improved. Li-Huei Tsai, director of the Picower Institute for Learning and Memory at MIT, and the paper’s senior author, said “If humans behave similarly to mice in response to this treatment, I would say the potential is just enormous, because it’s so non-invasive, and it’s so accessible.”

There have been a number of major setbacks in Alzheimer’s research where successful trials on rodents didn’t translated into benefits for humans, the most recent example being the Eli Lilly drug trial. However scientists say the efficacy of strobe lights should be quicker and cheaper to confirm in humans than drugs.

The study, published on December 7th in the Nature, hinges on the observation that Alzheimer’s causes a loss of synchronised brain activity, known as gamma oscillations, which is linked to attention and memory. To restore the activity, the scientists used mice that had been genetically engineered so that the neurons that generate gamma activity in the brain were sensitive to light. The technique, known as optogenetics, allowed the scientists to artificially cause groups of neurons to fire in unison by pulsing light into the brains of the mice.

After an hour of stimulation, the researchers found there was a reduction of about 50% in the levels of beta amyloid proteins in the hippocampus, the brain’s memory centre. Closer inspection showed the amyloid had been taken up by microglia, the brain’s immune cells. In a healthy brain microglia clear up unwanted compounds, but in Alzheimer’s microglia can lose this function and switch into an inflammatory state and secrete toxic compounds instead. Strengthening gamma oscillations appeared to switch the microglia back into a productive state.

The scientists then showed gamma oscillations could also be stimulated non-invasively in the visual brain region simply by exposing the mice to a flickering light. At 40Hz the flicker of the light is barely discernible and would be “not offensive at all” for a person to have in the background. After being given one hour of flickering light each day for a week, the scientists saw a 60% reduction of harmful amyloid plaques in the brains of the mice.

Ed Mann, an associate professor of neuroscience at the University of Oxford, said “I was surprised, and it’s exciting, that such a simple stimulus can target a molecular pathway and have such an effect in an hour.”

Questions remain as to whether boosting gamma oscillations and sweeping amyloid plaques out of the visual brain region would help with memory, which is centred in the hippocampus, or broader cognitive abilities.

David Reynolds, chief scientific officer at Alzheimer’s Research UK, said “It is conceivable that changing brain cell rhythms could be a future target for therapies, but researchers will need to explore how light flickering approaches could not only reduce amyloid in the visual area of the brain but in those areas more commonly affected in Alzheimer’s.”

The authors of the study suggest it may be possible to take a multi-sensory approach, using a combination of flashing lights and vibrating chairs. Li-Huei Tsai and Ed Boyden, a colleague at MIT and study co-author, have started a company called Cognito Therapeutics to pursue tests in humans.

There are 850,000 people with dementia in Britain and this figure is expected to reach 1 million by 2025. In 2016 dementia overtook heart disease as the leading cause of death in England and Wales.