Scientists have come up with various theories suggesting the reasons why we sleep. These theories tend to vary from expert to expert, with some believing sleep allows us to recharge our batteries. There have also been theories suggesting it’s a way for animals to avoid the threat of predators by keeping as still as possible, or the brain’s way of expelling waste. But two separate studies published earlier in the week tell us pretty much the same thing – sleep is necessary because it allows us to forget some of the day’s less important events and discoveries.
Esquire discussed one of these studies, which was published Thursday in the journal Science and theorizes that the reason we sleep is to “hit the reset button” on the brain’s synapses. Synapses are brain features that store memories and transmit signals between neurons, collecting more information through a person’s waking hours and growing in the process. But without sleep, there’s a chance for the brain to get overloaded with unnecessary information, and a good chance that the brain won’t be functioning at 100 percent of its potential.
Based on the University of Wisconsin-Madison researchers’ observations on mice, the tiny animals were able to hit that “reset button” on their brains while asleep, with synapse growth decreasing by an average of 18 percent. Larger synapses, however, remained at a similar size, suggesting that sleep doesn’t affect more important memories.
— Neuroscience News (@NeuroscienceNew) February 3, 2017
“Sleep is the perfect time to allow the synaptic renormalization to occur … because when we are awake, we are ‘slaves’ of the here and now, always attending some stimuli and learning something,” said study co-author Dr. Chiara Cirelli in an interview with Live Science. “During sleep, we are much less preoccupied by the external world … and the brain can sample (or assess) all our synapses, and renormalize them in a smart way.”
According to the New York Times, the UW-Madison study was the product of years of research, coming more than a decade after Cirelli and fellow UW-Madison biologist Dr. Giulio Tononi first suggested that synapses grow so much while people are awake, with the intense activity making our brains “noisy.” This theory has since been dubbed as “synaptic homeostasis.”
Meanwhile, another team of researchers was working on a similar study that sought to find out the reason why we sleep. The scientists in the second study, who were led by Johns Hopkins University postdoctoral researcher Dr. Graham Diering, conducted multiple experiments, also on mice, hoping to gather proof of synaptic homeostasis.
To this end, they treated mice with an agent that triggered surface protein activity within brain synapses, and while looking through a small “window” into the animals’ brains, they observed that surface protein levels had declined while the mice slept. That was a sign that there was indeed a shrinkage in synapses during sleep, but what proved more interesting was how Diering and his colleagues isolated one protein they found to be responsible for the pruning of synapses during sleep.
The protein, which was given the codename Homer1A, was shown to be a key factor in the paring back of synapses during neuron-in-a-dish experiments. And to further prove this, Diering’s team studied genetically engineered mice unable to generate Homer1A. These mice were able to sleep as non-engineered mice do, but synapse and surface protein activity didn’t change in a similar way.
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Even more interesting was how subsequent experiments saw mice injected with a neuron-blocking agent having “fuzzy” memories due to their inability to prune synapses while asleep, with the ordinary mice acting sharper once awake.
Russell Foster, director of the University of Oxford’s Sleep and Circadian Neuroscience Institute, told Live Science that he was especially impressed with the UW-Madison study. And while neither study was able to determine how the brain chooses which synapses to prune, Foster, who wasn’t involved in either paper, acknowledged that the pruning process is an important contributor to the reasons why we sleep.
“It is critical to have pruning back at night, so that the huge amount of information encoded by temporary synapses during the day won’t overwhelm the brain. Pruning ensures that only the most important information is retained.”
[Featured Image by SE Media/Shutterstock]