The Dalai Lama once said that sleep is the best meditation and I’ve often found this to be true; having gone to bed with a problem on my mind and waking up with the solution the next morning.

There is so much we still don’t understand about how our brains work and how exactly sleep aids in the process, but research has uncovered a number of interesting facts. What science does prove is that sleep is instrumental in the creation and retention of new memories.

Dr Matthew P Walker, director of the Sleep and Neuroimaging Laboratory in Boston, unpacks what we do know about sleep’s effect on the brain in this Google Tech Talk:

It’s quite a long talk so I’ve broken it down into its relevant segments here:

What is sleep?

From minutes 3 to 10 Dr Walker deals with the basics of what sleep is i.e. REM (Rapid Eye Movement) and NREM (Non-Rapid Eye Movement) sleep. NREM is further subdivided into four stages (1 through 4) with stages 3 and 4 providing the deepest sleep. While a person in deep sleep might seem to be complete dormant, this is actually the sleep phase where your brain is most active (more so than when you’re awake), making these stages of the nightly sleep cycle incredibly important. REM sleep on the other hand is the phase when most people dream.

A sleep cycle typically lasts 90 minutes during which the brain will alternate between REM and NREM sleep. You can learn more about how these cycles normally play out here.

What sleep does

Minutes 10 to 16 explores the known purposes of sleep by looking at the effects of pulling an all-nighter. This was done by conducting a simple experiment wherein both groups of students were awake during the first day, but that night one group was kept awake in the lab while the other got a full 8 hours of sleep. The next day the students are asked to cram a number of facts into their brains and are then quizzed two days later (after both groups were given the opportunity to sleep well for two nights).

The results? The sleep deprived students had a 40% deficit in their ability to make new memories. Research has shown that the part of the brain called the hippocampus is essential in forming new memories, but that it is impaired in people who are sleep deprived.

The Hippocampus – the Brain’s USB

Imagine that the hippocampus works like a USB stick – it can store information quickly, but has limited storage capacity. Sleep helps move the new memories stored in the hippocampus that day to the cortex (or hard drive), freeing it up to collect new memories the next day. Dr Walker points out that it also helps to sleep well after learning as it helps to ‘save’ the memories to the cortex.

Long story short – sleep allows the brain to sort the data it gained during the day, storing the relevant information in the right place. Sleep deprivation short circuits this process leading to memory loss / impaired brain function.