Sleep plays an active role in memory

20 June 2019

Interview with 

Anna Weighall, University of Sheffield

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When it comes to memory, the importance of sleep goes well beyond the negative impact of being tired. The process of sleep plays an active role in memory formation. So says Anna Weighall - cognitive psychologist from the University of Sheffield, and she spoke to Katie Haylor. First up, Anna explained how sleep helps to integrate new information learned that day into pre-existing information stored in our brain...

Anna - We, as human beings, children or adults can learn new information really quickly and easily. So, for example, we might learn a new word - I'll introduce one now, for example, hippocampus. Hippocampus is a little part of the brain the shape of a seahorse that's really important for memory and, in particular, when we learn something new, like the new word hippocampus we’ll initially store it there, so that happens while we are awake.

Imagine we've learnt this new word and now we need to put it in our mental dictionary with all the other words that we know already. Well what seems to happen during sleep is that the new words stored in our hippocampus, which is like a temporary bit of memory if you like, transfers into our long-term memory which is stored in the neocortex. And it looks as though sleep actually facilitates it helps the links between the immediate memory in the hippocampus and our long-term memory in the neocortex.

Katie - Can we see that effect happening in the brain waves?

Anna - Yeah. So, we can see it in several different ways. Thinking about the brainwaves, in a sleep experiment a researcher might invite participants to come into the lab to learn some information and then to stay overnight or to have a nap in the lab, so your brain waves will be recorded. We can then look the next day at how well the participant remembers the information they learned previously, and we look to see whether they remember more or less than they did before they went to sleep. And we can then look for associations between the brain activity, so how much of certain types of sleep did you have, and we can look for a relationship between that and how much you remember the next day. Spindles are little sharp spikes in the electrical activity that happen during that slow wave sleep. Neuroscientists believe that those are associated with transmission of information and the connections from the hippocampus to the neocortex.

Katie - So now we know why sleep is important for memory and learning, what effect can suboptimal sleep have then on someone's ability to remember something?

Anna- Not having enough sleep, or learning information and then not sleeping on it, might cause you to forget more of that information. It will depend, of course, on what that information is. Just occasionally having a poor night's sleep, I don't think we need to worry that that's going to drastically affect our memory. However, we do know that if people are tired, in the short term it will affect their performance on a given day so it might affect their ability to encode memory because they're tired. And, over time, if people are consistently sleep deprived then again that can affect their memory abilities.

Katie - Most people are probably aware of general sleep hygiene, things that are common sense, a good idea, sometimes difficult to implement. Does it go beyond that?

Anna - Especially with children and young people, encouraging them to have good sleep habits is a really good place to start. At the University of Sheffield, the hospital, and in collaboration with an intervention designed by the Children's Sleep charity, they've shown that you can actually improve sleep by as much as 2 1/2 hours. You can increase a child's sleep by as much as 2 1/2 hours where they've been experiencing difficulties and where the family becomes involved in an intervention that improves attitudes around sleep and bedtime behaviour. That's actually a much bigger improvement than we've seen in the leading trial using melatonin, which is a hormone that’s sometimes used to improve sleep.

Katie - If sleep is so important for learning and memory, is there anything about sleep that we can tweak to help us be better at remembering things?

Anna - This is a very exciting emerging area of neuroscience, I think, and we certainly still don't have all the answers. But a few researchers in a few labs now have demonstrated that you can actually change the properties of sleep using quite simple techniques. You can boost the power of slow wave sleep, the depth of the slow-wave so you make the slow-wave sleep perhaps last for longer and perhaps have more potential to affect learning and memory. So, you kind of make that deeper sleep even deeper perhaps is a way to think about it, using something called auditory stimulation. Monitoring somebody's brainwaves while they sleep and once they begin to enter a phase of slow-wave sleep they are played a noise,  pink noise, which if you've heard of white noise, pink noise is basically very similar, it sounds similar if you've heard it, it's just not quite as crackly. And what they do is synchronise the onset of this pink noise with the onset of the slow-wave sleep and by doing so you can actually see these sleep waves changing in a measurable way.

This is a very experimental technique and it needs further replication, but there is preliminary evidence that suggests that boosting slow-wave sleep in this way can be associated with increases in memory recall for information that you learnt before that sleep, so that's been shown in studies with adults. And there’s some very preliminary emerging evidence that there is potential for this sort of intervention in atypical populations, for example children with ADHD. So there's still a lot to learn, but if that finding bares out, then that's potentially very powerful intervention that might help people who have problems sleeping.

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