A new study has revealed that chronic sleep deprivation can actually cause the brain to eat itself. Michele Bellesi of the Marche Polytechnic University in Italy analysed the brains of mice who had regular sleep, spontaneous wake, sleep deprivation and chronic sleep deprivation. The results, published in the Journal of Neuroscience, found that the brain cells that destroy and digest worn-out cells and debris go into overdrive in mice that are chronically sleep-deprived.
While this may have beneficial effects in the short term – for example clearing debris could protect healthy brain connections – the long term effects look to be much more detrimental.
Bellesi and his team compared the brains of mice with varying levels of sleep. Four groups of mice were tested. The first group could sleep as long as they wanted, the second were periodically woken up, the third were kept awake for a further eight hours and the fourth had been kept awake for five days – simulating the effects of chronic sleep deprivation.
Using block-face scanning software, the scientists measured the synapses and cell processes in the mouse’s frontal cortex. The particular area of the brain that Bellesi investigated was glial cells, which form the brain’s housekeeping system. Previous studies had found that a gene that regulates the activity of these cells is more active after a period of sleep deprivation.
One type of glial cell, called an astrocyte, performs a range of functions including pruning unnecessary synapses to help rewire the brain. Another type, called a microglial cell, roams the brain for damaged cells and debris. After an undisturbed sleep, the team found that astrocytes appeared to be active in around six percent of the synapses in the brains of the rested mice.
With regards to the sleep-deprived mice, the researchers found their astrocytes to be more active. Those that had lost eight hours of sleep showed astrocyte activity in around eight percent of their synapses, while the cells were active in 13.5% of the synapses of the chronically sleep-deprived animals.
Therefore, the study shows that sleep loss can trigger the breaking down of the brain’s connections. Speaking to the New Scientist, Bellesi continued: “We show for the first time that portions of synapses are literally eaten by astrocytes because of sleep loss.”
It is not yet known whether this activity has a positive or negative effect in the long term. On the one hand, a large proportion of the remodelling was concentrated on the largest synapses which are used more intensively. ‘Pruning’ these may actually be beneficial, according to Bellesi.
On the other hand, the team also found that microglial cells were more active after chronic sleep deprivation. This is worrying, according to Bellesi, because excessive microglial activity has been linked to a range of brain disorders. This may explain why a chronic lack of sleep increases people’s risk of Alzheimer’s and other forms of neurodegeneration, but more research is required to discover just how long the effects of sleep deprivation last.