A team of researchers, led by neuroscientist Michele Bellesi from the Marche Polytechnic University in Italy, have concluded that prolonged periods of sleeplessness can cause the brain to demolish and digest its own neurons and synaptic connections.
This is a process that occurs normally during sleep, when a glial cell called an astrocyte will gobble up superfluous synapses. The astrocyte works alongside the activity of a microglial cell, which will clear the toxic byproducts of neural activity through a process of phagocytosis (literally: “to devour”). Together, they will prowl the organ and, essentially, conduct nightly maintenance to keep the complex network of your brain in order.
After a period a chronic sleeplessness, however, the astrocyte and microglial cells go into overdrive, to the extent that they may do harm to the brain. Think of it as frantic housekeeping, when the brain throws out the dishes along with the stains.
Studying the activity of mice, Bellesi and his team found that well-rested subjects have astrocytes active in around 6% of the synapses in their brain. For mice that had lost eight hours of sleep, however, that activity level was 8%. For those that were kept awake for five days straight, that figure rose to 13.5%. “We show for the first time that portions of synapses are literally eaten by astrocytes because of sleep loss,” Bellesi told New Scientist.
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This alone may not necessarily be a bad thing. Bellesi said that it seemed much of the astrocyte activity in sleep-deprived mice was around larger synapses – which are “like old pieces of furniture, and so probably need more attention and cleaning.”
What’s more worrying is the increase in activity of the microglial cells, which has been linked to a variety of brain disorders including Alzheimer’s. There have been a number of studies into how a lack of sleep could accelerate development of the toxic plaques that cause Alzheimer’s disease, so it could be the case that overactive microglial cells leave the brain vulnerable to these problems.
There remain many questions, however. This study was conducted on mice, so it’s not known if the same activities are set off in the human brain. It’s also not known how long these effects last, and whether a good night’s sleep can stem the damage. The researchers intend to continue their work in the area – which comes at a time when sleep problems, and sleep monitoring, are very much in the public consciousness.
The researchers’ full study is published in the Journal of Neuroscience.