In December, researchers were able to reverse the effects of Alzheimer’s disease in mice using a flashing light. What’s more, this might tell us something about what consciousness entails in the human brain, and what gamma waves may have to do with it.
Plaques, tangles, and gamma
In order to understand anything about how important this development is, we need to know some things about Alzheimer’s and how it works. Alzheimer’s is a neurodegenerative disease which accounts for the majority of dementia cases. It normally develops after age 65 and worsens over time, leading to problems in memory, thought processing, and behavior. To be clear, Alzheimer’s is not a normal part of aging; it’s normal, for example, for an older individual to forget that their daughter was going to visit them that day, but not for them to forget who their daughter is. Tragically, there is no known cure for Alzheimer’s, but diet and exercise might help slow its progression (for more on the benefits of running as Alzheimer’s prevention, click here, and for more on architecture designed to help dementia patients navigate spaces, click here).
Scientists suspect that the culprit behind Alzheimer’s is the buildup of two toxic proteins: beta amyloid between cells (called “plaques”) and tau within cells (called “tangles”). Most people develop plaques and tangles as they age, but Alzheimer’s patients develop more of them in specific patterns, and in areas key for memory formation and maintenance. This makes them good markers for determining the disease’s progression.
Even before these plaques, tangles, and other symptoms begin to develop, there is another telltale sign of Alzheimer’s: disrupted gamma waves. When brain cells are in sync and fire in a rhythm, they produce waves of electrical activity. Waves of different frequencies are associated with different types of brain activity, but gamma waves (with frequencies between 25 and 100 Hz) are associated with alertness and concentration. Up until now, researchers thought that the decrease in these gamma waves in Alzheimer’s patients was just another side effect of the disease. This is where things get interesting.
Suspecting that gamma might have more to do with the disease, researchers programmed mice to develop Alzheimer’s and looked at their brain activity while running in a maze. This was before plaques, tangles, and other observable symptoms had formed, so unsurprisingly, they found that the mice’s brains had disrupted gamma waves. What had not yet been shown is that gamma can directly influence the formation of beta amyloid later in the disease’s progression. So, they decided to create the waves themselves by stimulating brain cells at a gamma frequency using optogenetics, a method which uses light to stimulate cells by way of a virus that causes sensory receptors to become light-sensitive. They used this method in a part of the hippocampus called CA 1, a well-studied brain area involved in long-term memory formation and maintenance. They found twice as many microglia—cells involved in reuptaking beta amyloid—and that up to 50% of the beta amyloid in CA 1 had been reduced after only an hour of stimulation!
Here is a quick, 5-minute summary of the study from the Picower Institute for Learning and Memory at MIT.
But that’s not all. Stimulating brain activity in this way is very invasive (it involves drilling a hole into the skull, injecting the virus, and implanting a light), so researchers wanted to make this method more practical. They wondered what might happen if pre-Alzheimer’s mice looked at a flashing LED light at that same gamma frequency. Lo and behold— they found the same reduction in beta amyloid and increase in microglia, this time in the visual cortex. Researchers immediately began speculating that this might be a viable treatment option for those with Alzheimer’s disease.
Shedding light on gamma
Now before you go out and buy yourself a strobe light, note that we should be careful in interpreting these results and the potential implications for Alzheimer’s treatment. Most studies done on mice fail in clinical trials on humans, because the disease does not exist in mice and it is difficult to genetically modify them to have Alzheimer’s-like symptoms. We therefore cannot tell whether treatment would directly alter observable symptoms like memory loss. There may also be problems with extending the effects of such a treatment, as the mice in this experiment benefited most from the accumulation of light over several days.
Alzheimer’s entails the loss of everything we think of as consciousness: the formation and retrieval of memories, the ability to pay attention, the use of language and orientation, and the perception of the world around us.
Having said that, this study may additionally shed light on the role that gamma waves play in the brain, as previous research has shown that gamma is involved in memory retrieval and attention, among other cognitive processes. After all, Alzheimer’s entails the loss of everything we think of as consciousness: the formation and retrieval of memories, the ability to pay attention, the use of language and orientation, and the perception of the world around us.
Could we interpret this breakthrough as more evidence that gamma is the key to understanding consciousness? Many researchers would say it is not, as some studies have suggested that gamma is nothing more than filtered noise, which just indicates that neurons are active and firing. Regardless of whether gamma is a direct measure of whatever neural processes consciousness entails, this study shows that gamma could still be a good measure of it. What is more, it is a measure we can affect with relative ease. Knowing this may help us study consciousness and the role that gamma waves play in its formation.