Have you ever stayed up late cramming for a test? Perfecting a presentation? Finishing a paper? Most of us have been there. Studies show, however, that we may have been better off by going to bed.

Studies on the links between rest and cognitive performance were being done as early as 1924, when American psychologists John Jenkins and Karl Dallenbach asked students to memorize lists of random syllables. The students’ memories were then studied one, two, four and eight hours later. They found that the longer the students slept between the learning session and the tests, the better their ability to recall more of the syllables (source).

A more recent study at the University of Exeter in the UK discovered that sleep almost doubles your chances of remembering previously unrecalled material, validating the theory that memory sharpens overnight.
Bottom line: If you’re staying up late cramming for an exam or presentation the night before, your chances of retaining that information are much lower with less sleep.

Simply put, while you rest, your brain is hard at work processing all the information you’ve encountered during the day and encoding them into memories. For this to happen, three functions have to occur:

1. Acquisition– the learning or experience of something new

2. Consolidation– the memory achieving stability in the brain

3. Recall – the ability to access that memory in the future

While acquisition and recall both occur while you’re awake, it’s now widely believed that sleep plays a crucial role in the consolidation of a memory, regardless of what type of memory it is. This new state makes the memory much less susceptible to interference (source).

A good night’s rest also requires the proper balance of both NREM (non-rapid eye movement) and REM (rapid eye movement) phases of sleep, as both play separate roles in the stages of learning and memory formation. At the University College of London, Professor Vincent Walsh explains that the slow-wave sleep (NREM) we experience earlier in the night is responsible for the consolidation of information we acquire that day, or declarative memory. This is the knowledge of fact-based information, like remembering what you had for lunch.

The brain spends the later part of the night in REM sleep, focusing largely on procedural memory. This is when we remember how to do something, such as play the piano. This is also the time when our brains perform subconscious creative problem solving (source).

The relationship between REM sleep and procedural learning consolidation, particularly involving sensory and motor related tasks, has been – and continues to be – the topic of many recent studies. One study involving the testing of finger-tapping saw people split into two groups. After training, both groups were tested with or without intervening sleep. The group that was allowed to sleep displayed a post-training increase in both accuracy and speed; the group that stayed awake showed no signs of improvement.

It is also currently being hypothesized that REM sleep additionally plays a role in declarative memory processes if the information is more complex. For example, individuals engaged in an intensive language course experienced a marked increase in REM sleep (source).

These results all give further validation to the synaptic homeostasis hypothesis of sleep, developed in 2003 by scientists at the University of Wisconsin-Madison. This hypothesis, known simply as SHY, seeks to explain why our brain needs rest after a day spent learning new information. During waking hours, as we saturate our brains cells with information we strengthen the synapses that form connections between those cells. It’s an exhaustive process, but sleep allows the brain to consolidate those memories (source).

Christoph Nissen, a psychiatrist at the University of Freiburg, conducted a series of tests on both men and women, either after a night of sleep or a night without sleep. In the initial round, Nissen used magnetic pulses to make neurons fire in the volunteers’ brains, causing a muscle twitch in the left hand. When performed on the sleep-deprived group, a far weaker pulse was enough to elicit a muscular response.  The implication is that a sleepless brain is in a more excitable state, with a stronger connection between neurons.

Nissen then used brain stimulation to mimic the firing of neurons that occurs during the consolidation of memories. The neurons were much less responsive for those in a sleep-deprived state, suggesting that the wiring of new memories into the brain is impaired by sleep loss.

When considered together, the test results suggest that rest allows brain activity to quiet so memories can be consolidated.  The sleep-deprived group, by contrast, showed a level of electrical activity that notably blocked the formation of new memories (source).

So what happens when we try to get by on less sleep? Not only are we less able to focus and receive information, but our strained neurons can no longer coordinate information properly, and our faculty for accessing previously learned information becomes largely impaired.

Sleep deprivation doesn’t just hurt your memory – it can also make you more susceptible to false recall and manipulation. In one study, participants who got less than 5 hours of sleep a night were much more likely to claim they had seen a news video they hadn’t than their well-rested counterparts. They were also more likely to incorporate false information given to them by the researchers into their own personal recall (source, p.107)

So the next time you’re tempted to burn the midnight oil, ask yourself – is it worth it? Maybe not.