Researchers pinpoint how deep sleep affects learning

Studying all night is a popular way to cram for an exam, but your synapses will thank you if you use the time to sleep instead. Keystone

Scientists have long known that sleep and learning ability are connected, but for the first time, researchers in Zurich have shown exactly how this causal link works in an experiment with human test subjects.

There is plenty of scientific evidence linking deep sleep and learning, but you may have experienced this relationship first-hand if you’ve ever pulled an all-nighter to study, only to find yourself struggling to remember exam answers the next day.

Now, thanks to a non-invasive experimental technique, researchers at the University of Zurich and the federal technology institute ETH Zurich showed how interfering with deep sleep in certain areas of the brain affected learning ability in 13 human test subjects. The results were published Monday in the journal Nature Communications.

Sleep sound

In their experiment, the researchers had seven male and six female test subjects learn three separate sequences of finger movements during the daytime. At night, the researchers monitored electrical activity in the brains of these subjects during sleep using a non-invasive tool called an electroencephalogram (EEG).

At certain points, the researchers used acoustic (sound) stimulation to disturb deep sleep in the regions of the subjects’ brains responsible for motor tasks – but this interference was subtle enough that the subjects were totally unaware of it.

Sure enough, the researchers found that the test subjects made more mistakes and displayed more difficulty in reproducing the finger movements they had learned following this interference, compared to when their sleep had not been disturbed.

The reason for this, as described by the researchers, is fairly intuitive: without adequate downtime to recover during the night, the subjects’ synapses – the connections between their brain cells – simply became overwhelmed with environmental stimuli.

“In the stimulated regions of the brain, the capacity to learn was saturated, which prevented the learning of certain motor tasks,” explained ETH Zurich professor and co-author Nicole Wenderoth in a statement on Monday.

These results were compared to those from a control group, in which the acoustic disturbance was targeted at a different region of the brain not associated with motor tasks. In this case, the interference had no effect on the subjects’ ability to reproduce the finger movements.

Clinical applications

The researchers hope that this new knowledge of exactly how deep sleep and learning are linked will be key for future clinical studies, as many human diseases – for example, epilepsy – also manifest themselves during sleep. The new method could be used to manipulate certain brain regions during sleep to help improve patient conditions.

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