Scientists May Have Solved First Half of Sleep Mystery

Neuroscientists have revealed new details about how our brains are reset when we sleep. But their findings open new questions about the role of sleep in the second half of the night.

Getting enough sleep is essential for our mental and physical well-being, but scientists are only just beginning to figure out what is happening in our brains when we sleep. Many neuroscientists agree that sleep plays an important role in “resetting” our brains at the end of the day, and new research from University College London has revealed exciting neurological data to support this theory.

“When we are awake, the connections between brain cells get stronger and more complex,” Jason Rihel, a professor in cellular and developmental biology at UCL and the lead author on the study, said in a statement. “If this activity were to continue unabated, it would be energetically unsustainable. Too many active connections between brain cells could prevent new connections from being made the following day.

“While the function of sleep remains mysterious, it may be serving as an ‘off-line’ period when those connections can be weakened across the brain, in preparation for us to learn new things the following day.”

In their new study, published in the journal Nature, Rihel and his team used specially designed zebrafish to study the activity of brain cells during the sleep-wake cycle. Specifically, they were interested in the connections between the brain cells, called synapses, which allow information to be passed from one cell to another.

After several sleep-wake cycles, the team saw that the brain cells consistently gained more connections during the waking hours, and lost them during sleep. However, these rearrangements mostly happened in the first half of the animal’s nightly sleep session.

“Our findings add weight to the theory that sleep serves to dampen connections within the brain, preparing for more learning and new connections again the next day,” first author Anya Suppermpool said in a statement. “But our study doesn’t tell us anything about what happens in the second half of the night.”

So why is it important that we get our full eight hours?

“There are other theories around sleep being a time for clearance of waste in the brain, or repair for damaged cells—perhaps other functions kick in for the second half of the night,” Suppermpool said.

More studies are needed to confirm these results in humans, but this one offers exciting insights into the neuroscience of sleep and brings us one step closer to understanding why it’s so important to get your ZZZs.