Author: Nina Wycech // Editor: Luke Marshall

How long did you sleep yesterday? Have you pulled an all-nighter or sacrificed sleep to study longer? As a neuroscientist interested in sleep, your answer might scare me. But at the same time, I know that the choice to sleep or to study is more complicated. It’s difficult to stop learning when we want to do well. But what if I told you, that sleeping might help you more than extra hours of studying?

Before we delve into my argument, let’s think about learning. One crams at the library, makes memory cards, completes practice questions etc.

Step 1: Learning and memory acquisition – requires understanding the content.
Step 2: Remembering – requires memory consolidation, forming new memories. It’s also important to note that we need to hold on to that memory – we can’t forget it, at least not before our exam. The information needs to be reliably rooted in our brain (memory stabilisation). After a few hours, one is likely to reach the plateau of learning, when our performance can’t be further improved – the memory can’t be further enhanced.
Step 3: Finally, the memory needs to be recalled during the time of the trial.

Sleep can help you to have the mental capacity to learn and recall your knowledge during the exam. Arguably, it is step 2 – memory consolidation – that is the key to success, bridging the hours in the library with success at the exam.

Tap, tap through the night

Firstly, I admit that memory stabilisation happens throughout the day when we are awake. However, the next stage of memory enhancement does require sleep, which has been clearly outlined in numerous studies.

In a study by Dr Matthew Walker, known for his book “Why We Sleep”, two groups of people were taught a finger tapping sequence – one at 10 am and, the second at 10 pm. Both groups were consistent with diligent students and improved during their learning sessions. After 12 hours of being awake for the first group and sleeping for the latter, both were tested again. The night of sleep caused the second group to improve in both speed and accuracy. Even though the same amount of time has passed, the first one showed no change in performance, until after their chance to sleep throughout the night. That suggests that it is not simply the passage of time that forms the basis for memory enhancement, but a night of sleep.

Of note for all the language students, another study by Dr Fenn and colleagues from the University of Chicago showed the same importance of sleep in learning, this time in understanding synthetic speech. Synthetic speech is artificially generated and aimed to mimic human speech. Those foreign speech patterns are initially problematic to understand, though they became easier the more words the participants heard (no words were repeated). Such studies were repeated with various memory tasks, not limited to understanding or motor processing. In one example, participants had to recall a word-pair association after sleep. The improved recall after sleep came as no surprise, though the discovery that it depended on the participants expecting to be tested later on was novel. Turns out that sleep tends to enhance our memory more when we expect it to be useful in the future. Finally, further studies have found that the first night after learning is of particular importance, but further nights still provide some benefit.

Memories on Loop

The activation of the brain during sleep has been long studied, mostly using electroencephalogram (EEG) recordings. The probes are attached to an individual’s head, measuring the activity at certain places within the cortex. Intracranial recordings also measure the activity within the cortex, though with probes placed inside the skull. By employing those techniques in the studies of memory and sleep, scientists showed that the brains of the participants activate in a similar pattern during both acquiring and remembering information learned during the day. The pattern of activity is replayed throughout the night, as the sleep progresses through stages. Moreover, the investigators were able to decode which images the participants had seen – horses or faces – simply by analysing the pattern of the activity during sleep. Intriguingly, they also found a way to use the pattern of activation to boost memory enhancement. They used a technique called targeted memory reactivation. While participants were learning, the overseers presented them with cues – e.g. Smells or sounds – at the sleep stages associated with remembering. The same cues were later presented during their sleep, evoking a response in brain activity and thus strengthening the neural connections involved. As neuroscientists say – what fires together, wires together.

For the smart-watch aficionados: What stages to watch for

The phases of sleep are repeated roughly every 90-120 minutes and consist of rapid eye movement (REM) sleep, and 4 distinguishable phases of non-REM (NREM 1-4)*. These phases are not distributed equally throughout the night, and their pattern is best understood by examining graphs or watching a wonderful TED talk by Dr Walker. The proportion of different phases, regarded as sleep architecture, is influenced by many factors, such as sleep history, alcohol, medicines, marijuana, stress, or diseases. To be on the safe side, I’d recommend not skipping any of the phases, especially during the exam period.

Using much bulkier equipment than the smartwatches, Dr Walker and colleagues measured the sleep stages and correlated their length with their results. As it turned out, the more NREM 2 stage they had, the better their learning outcomes were. In turn, it is hypothesised that REM sleep is crucial for the enhancement of the emotional declarative memory e.g. Remembering facts or stories that evoke certain emotions. As shown above, NREM 2 occurs more early in the night, while REM dominates later on.

*In alternative naming, NREM 3 + NREM 4 are collectively regarded as NREM 3 on the 1-3 scale, as slow wave sleep (SWS) or deep sleep. NREM 1 + NREM 2 together are called the “light sleep”.

To put this to bed

There remains plenty more to be said about sleep, and plenty more left to yet be discovered. What we now realise, is that sleep is crucial for homeostasis, affecting almost every aspect of our health. Thankfully, the information about it tends to stay with you – once you’ve learned it, you’ll never disregard sleep again.

So: Good luck with your exams. Don’t forget to sleep.

Bio: Nina Wycech

Pronouns: she/her
I consider myself a collector of fun facts and interesting stories – which often come from science. I’m somewhat of a scientist myself. I graduated B.Sc. Neuroscience from UoM and I’m currently continuing my education at Glasgow doing an M.Sc. in Bioinformatics. My favourite subject is sleep & circadian rhythms, but I’ve been exploring genome sequencing extensively throughout my study.