08 February 2018

Turn on the light brighter

Dim light makes it sillier, and flickering with the right frequency cures Alzheimer's

Ivan Sychev, Geektimes

Prolonged exposure to poorly lit rooms changes the structure of the brain, reduces the ability to learn and impairs memory. Neurophysiologists at the University of Michigan found this out using experiments on mice: a group of animals that received little light for a month lost 30% of the capacity of the hippocampus, responsible for the transition of short-term memory into long-term memory.

Researchers from the University of Michigan used Nilotic grass mice for experiments on the effect of light on the brain. Like humans, these mice are diurnal and sleep at night. The animals were divided into two groups. The first group was exposed to dim light, and the second group had more than enough light. As a result, scientists found out that mice from the first group lost 30% of the capacity of the hippocampus and poorly performed the spatial task assigned to them. Mice from the second group performed this task with ease. Fortunately, the process turned out to be reversible: four weeks of bright light after a month–long break - and the first group fully recovered their abilities. 

This is the first study that has shown structural changes in the brain depending on the light mode. The inability of mice exposed to dim light to solve a spatial problem is similar to how people after a movie theater or a long shopping trip cannot find their car in the parking lot. Americans spend about 90% of their time indoors. 

Sustained exposure to dim light led to a significant reduction in the neurotrophic factor of the brain – a protein that stimulates the development of neurons. The BDNF protein increases the number and differentiation of new neurons and synapses, it is active in the hippocampus, cerebral cortex and forebrain, that is, in the areas responsible for learning and memory. When there is a lack of light, the body produces less of this protein, as a result of which fewer neurons and synapses between them are produced in the hippocampus. 


Dendritic spines of mice that spent a month in dim light (bottom) and control group animals (top) – VM.

Light acts on other parts of the brain before the production of BDNF in the hippocampus slows down. The team of researchers tested another area of the brain that can influence these processes – the hypothalamus. It produces the peptide orexin, which affects various brain functions. Scientists are faced with the question: if mice are given orexin, will their brains recover without a normal light regime? 

The answer to this question may open up new possibilities for the treatment of glaucoma patients, people with retinal degeneration and cognitive impairment. "In the case of people with eye diseases, can we directly manipulate this group of neurons to provide them with the benefits of bright lighting? Another possibility is to improve cognitive function in the elderly and people with neurological disorders. Can we help them restore their functions or prevent their further decline?" – says Lily Yang, head of the research project. 

Light can also affect degenerative diseases of the brain. In Alzheimer's disease, large deposits of beta-amyloid are formed in the neurons of the brain. You can reduce the impact of the disease if you reduce the production of these proteins. A team from the Massachusetts Institute of Technology did this by stimulating the hippocampus at a frequency of 40 Hz for an hour. Light pulses, which were fed directly into the brains of mice via optical fiber as part of the experiment, helped generate gamma rhythms of the brain, which are disrupted in Alzheimer's disease. At the same time, the production of beta-amyloid decreased by 40-50%.


Soluble beta-amyloid particles (green) in the brain of a mouse model of Alzheimer's disease (left). Hourly stimulation with random frequencies of flashes of light increases the amount of the peptide (in the middle), and flashes with a frequency of 40 Hz noticeably decrease (on the right). Figure from the article by Iaccarino et al. (Nature, 2016) – VM.

Since it is not a good idea to inject optical fiber into the brain of people in the hospital, scientists tried to find another method. It turned out that gamma rhythms can be corrected using LEDs. In mice that were forced to look at their flicker, not only the amount of beta-amyloid decreased by more than 2 times, but also the already existing amyloid plaques decreased. In the brain, with the right gamma rhythms, mechanisms were activated that eliminated deposits themselves.

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