How Sleep Improves Memory

This story originally appeared in the 2022 issue of Contours, the Faculty of Science magazine.

We spend about one-third of our lives asleep, a fact that has long-intrigued human scientists — like U of A psychology professor Clayton Dickson — but that figure wouldn’t impress most of the animal kingdom. Cats and dogs spend half of their lives snoozing, while bats and walruses spend three-quarters of their lives asleep. The sleepiest animal may be the koala, which can slumber for up to 22 hours a day.

But why we animals sleep remains a mystery. One hypothesis, Dickson says, is that sleep allows the brain to solidify new memories. In his Brain Rhythms Lab, he and his students study how brain activity during sleep aids in memory processes — kind of moving new memories into long-term storage. Often, this work involves rats, which cycle through different phases of sleep much like humans do. In a recent webinar, Dickson shared new research from his lab and explained how brain rhythms during sleep may play a role in memory. Here are a few takeaways.

1: Our brains are never truly at rest

Unlike a computer that you can power down at the day’s end, the brain experiences non-stop electrical activity, but in the form of nerve impulses passing between neurons. In fact, during sleep, the brain can be more active than when we’re awake, and certain activities, including some that might benefit memory processes, are thought to only happen during sleep. Dickson says this could be because sleep “frees the brain to do things it might not otherwise be able to do if it was performing its typical sensory- motor function.”

2: Studying brain waves could help unlock the mystery of memory

The movement of electrical signals through our brains offers clues to understanding what’s happening inside our heads, especially as we snooze. Dickson’s lab found that during deep sleep, two areas of the brain linked to memory (the hippocampus and medial prefrontal cortex) seemed to be on co-ordinated wavelengths — or, talking to each other using slow rhythms. Better understanding the synchronization of these rhythms could help uncover mechanisms involved in memory formation.

3: Going ‘offline’ is crucial for some brain functions

When we’re awake, our brains are busy processing sensory input from our environments and regulating our behaviour. Just as a computer can’t run Zoom while updating its operating system, our brains need to be “offline” for certain tasks. One of these tasks, says Dickson, could be consolidation, in which our brains download important information into permanent storage.

In a recent study in Dickson’s lab, researchers placed rats (natural swimmers) in a circular pool of water with a hidden platform that would allow them to rest from paddling. Once they had found the platform, rats could find their way back to it using visual clues they’d remembered — but how quickly they did so depended on what they did between trials. Rats who slept between trials remembered the route better than those who spent their break awake.

4: ‘Slow-wave sleep’ helps consolidation

A certain phase of sleep — slow-wave or deep sleep — is beneficial to memory consolidation. During this part of the sleep cycle, our heart rate and breathing slow, and our brain waves are at their slowest. Researchers are still figuring out what happens to our brains (and why) when we get under the covers.

But the more they unravel about this unconscious process, the closer we get to understanding our behaviours and abilities while we’re awake. Dickson’s lab’s work means the solution to the puzzle is more than a distant dream. 

Visit the Science Talks webinar page for links to this and other webinars.