We learn while we sleep – Link discovered between slow brain waves and learning success

If you want to pass an exam, be sure to get some good sleep before-hand. Because in sleep the brain processes and consolidates newly learnt matter. This is revealed in a new study shortly to be published in Nature. The study was supported by the Swiss National Science Foundation (SNSF).

As soon as deep sleep sets in, the brain cells start working in concord. Like football fans raising their hands in unison during a Mexican wave, millions of individual brain cells respond simultaneously with an electric signal. They thus generate the regular, low-frequency brain waves that are characteristic of deep sleep. Until now, the purpose of this brain activity was largely unknown. The shortly to be published study puts this function in a new context. Slow brain waves appear to consolidate and reinforce freshly learnt matter, explains Reto Huber, who conducted the study at the University of Wisconsin laboratory of Giulio Tononi in Madison, USA. The study is due for publication in the prestigious science journal Nature* on 1 July. Reto Huber holds a grant from the Swiss Foundation for Medical-Biological Scholarships (SSMBS) that was financed by the Swiss National Science Foundation.

For the purpose of the study, Reto Huber set 12 subjects a special learning task and then measured their brain activity during sleep. The subjects first had to accomplish a learning test on a computer. The basically simple task consisted of using a mouse to move the cursor to a set point on the screen. Subconsciously, however, they were learning new motor skills, because what the subjects did not know was that the computer was programmed to generate a slight aberration in the direction of the cursor movement, which they had to compensate for by modifying the mouse movements. Moreover, since their hand was covered during the experiment they did not realize the computer was playing tricks on them. Conscious learning very often involves many areas of the brain, which would have made it much harder to demonstrate local activation, explains Huber.

Such unconscious motor skills learning takes place in a small, thumbsized region of the right cerebral cortex, as other researchers have already shown. Reto Huber now wanted to find out whether this region of the brain displayed any special activity during sleep. To this end, he recorded the brain wave activities of the study subjects in their sleep by means of 256 electrodes attached all over their heads.

The large number of electrodes enabled Huber not only to register, but also to pinpoint the precise location of brain activity.

The deeper you sleep, the better you learn

And indeed the young Swiss researcher discovered what many brain researchers considered impossible. We noticed larger slow brain waves in the area of the brain that had been used for the test and nowhere else, said Huber. Not only that. The subjects who were most successful at mastering the test the next morning were also those whose brains had produced especially large slow waves during the night. The night-time brain waves seemed not only to have consolidated, but also to have enhanced performance in the computer-based test. Our study provides the first evidence that sleep plays an important role in learning processes, concludes Huber.

Scientists are still largely in the dark about the processes that actually take place in the brain during sleep at night or an afternoon nap. In particular, what happens at synapse level is largely unknown. Sleep researchers are considering the possibility that nighttime brain activity tests and sorts out newly created synapses. Important synapses would be retained and reinforced, unimportant ones disconnected. The slow brain waves may be performing a functional test of the synapses, says Huber.

Alexander Borbély, the Zurich sleep scientist under whose tutelage Huber obtained his doctorate, is impressed by these latest results. They prove that sleep can have highly localized effects on the brain. I believe these are very important findings.