Filing in your sleep

We put a lot of effort into memorising things (specially if we’ve learned some effective memory techniques!), and we naively expect that to be enough. But if your brain hasn’t filed away the information properly, all your efforts could be wasted. As you’re no doubt aware, a lot of things happen ‘behind the scenes’, and without your conscious awareness. But according to a study published in the Journal of Neuroscience by researchers at the University of York and Harvard Medical School, what happens when you’re fast asleep plays a big part in the process.

EEG machine

Electroencephalogram machine. A device that records electrical activity in the brain, and displays the result on a screen or a printout. EEG machines are used for both medical diagnosis and neurobiological research.

The study involved volunteers learning new words to increase their vocabulary. The words were studied in the evening, after which the volunteers were tested. They then spent the night sleeping in the lab, during which their brains were monitored with EEG machines. In the morning they were tested again, and they performed better in that test than in the one done immediately after the evening study session. The study demonstrated that they now knew more of the words they’d studied, and recognised them quicker, so the sleep had apparently assisted the learning and/or the memorisation process.

Another group underwent the training in the morning and were tested the same evening, with no sleep in between, but their second test didn’t show any marked improvement. The EEG results of the first group (the ones who had a night’s sleep before the second test) showed that deep sleep (slow-wave sleep) had been instrumental in strengthening the new memories, rather than rapid eye movement (REM) sleep or light sleep. It seems that sleep spindles played an important part in the process.

Sleep spindles

EEG readout

Sleep spindles indicate brief but intense memory activity, and may contribute to the integration of new memories

Sleep spindles are brief bursts of intense mental activity that occur when information is transferred from one memory store to another in the brain. The transfer takes place between the hippocampus, deep in the brain, and the neocortex, at the surface. Memories in the hippocampus are stored in an isolated, unconnected way. Memories stored in the neocortex, on the other hand, are stored in a vast network of connections, with many memories connected to one another.

The volunteers who had the benefit of a night’s sleep between the tests (and particularly those who had experienced more sleep spindles) demonstrated that they had more successfully connected the new information to information they already had. The had integrated it, forming new connections, which is exactly what you want when you learn new information.

The researchers had suspected that sleep played a part in integrating new memories, but now had some evidence to back it up. As Professor Gareth Gaskell, of the University of York’s Department of Psychology, said:

“We suspected from previous work that sleep had a role to play in the reorganisation of new memories, but this is the first time we’ve really been able to observe it in action, and understand the importance of spindle activity in the process.”

This study backs up what we’ve all long suspected – that a good night’s sleep plays a vital role in integrating whatever you’ve studied. And what it does show, quite clearly, is that sleep spindles play a vital role in that process.

Don’t short change yourself on sleep

As we all know, learning new things is only part of the big picture. You also have to memorise them, and integrate them with what you already know. If you only take care of a part of the process, your efforts might be wasted.

At the risk of stating the obvious, do yourself a favour and don’t skimp on your sleep. And don’t underestimate the importance of it . Regarding it as ‘dead’ time is a big mistake. While you appear to be doing nothing while you’re asleep, your brain is, in fact, very, very busy, and doing very important work.


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