Sleep and Memory

Sleep is essential for our brains to forge new connections and help with memory retention. At least two processes are at work while we sleep. Firstly, sleep helps to protect new memories from the disruptions that are inevitable during the day. And secondly, sleep consolidates memories according to their importance.

Recent research has shown for the first time that sleep resets the steady build-up of connectivity in the human brain that takes place during our waking hours. The study showed that the loss of a single night’s sleep was enough to block this natural reset mechanism. This led to the brain’s neurons becoming muddled with electrical activity and prevented new memories from being laid down properly.

This is also a boost for what is called the synaptic homeostasis hypothesis (SHY) of sleep, which was developed by scientists at the University of Wisconsin-Madison in 2003. The hypothesis states that when we’re awake, the synapses that form connections between brain cells strengthen more and more as we learn. Eventually our brains become saturated with information and this requires a lot of energy. Sleep is essential to allow our brains to wind down and consolidate our memories.

Looking at these results together, it’s clear that sleep allows the brain to calm its activity so memories can be consolidated and ‘written down’. The consequences of a loss of sleep were clear from the research study. Volunteers that had a full night’s sleep did far better in a simple memory test than those that had been deprived of sleep. The study also took blood samples from the volunteers and found that those who had been deprived of sleep had lowered levels of a molecule called BDNF (brain derived neurotropic factor), which regulates synaptic connections in the brain.

And it’s not just sleep in general that’s important – the specific stages of sleep also have important roles to play when it comes to brainpower. Slow-wave sleep (SWS), which is deep sleep has a significant role in promoting declarative memory. This is where our brains process and consolidate newly acquired information. During REM sleep, we consolidate procedural memory – the remembering ‘how’ to do something (such as riding a bike). Other aspects of sleep also have their own roles. Motor learning depends on the amount of lighter stages of sleep, while certain types of visual learning seem to depend on the amount and timing of both SWS and REM sleep.

Sleep is, in essence, essential in allowing our brains to learn new things during the day, whilst still preserving and consolidating old memories. Without enough sleep our memory retention is severely impacted. For more reading on this subject, try these books:

The Secret World of Sleep: The Surprising Science of the Mind at Rest (Macmillan Science)

Sleep and Brain Activity