It is not advisable to cram in learning material during sleepless nights and to arrive at examinations in a sleepy state. Instead, you should portion out the material well, sleep on it each time and approach an exam well rested. That’s when your ability to concentrate is at its best.
It is less practical to study while asleep. In fact, there have been experiments in which test persons were presented with word pairs during deep sleep. Although they were not consciously aware of them, they performed slightly better in memory tests afterwards. The learning effect was small, however, and it disappears altogether when one wakes up because of the noises and disturbs the recovery effect of sleep. Incidentally, the experiment shows that the brain can also register what is happening around it in a state of sleep. Biologists suspect that this is a protective mechanism against threats that has developed in the course of evolution.
The clearing work in memory takes place during the deep sleep phases, which we enter for the first time after falling asleep. Deep sleep is characterised in the EEG (electroencephalogram) by slow waves in the cerebral cortex. The neurons slowly alternate between an active and inactive state, reducing the strength of synaptic connections. An episode of deep sleep is followed by what is known as rapid eye movement or REM sleep, during which the nerve cells are once again active throughout. The cycle of deep sleep and REM phase repeats about four to five times every night. As we age, the deep sleep phases shorten, as does the ability to learn.
The purification of nerve cell connections during sleep is also known in sleep research as “synaptic homeostasis”. What happens biochemically in detail, how the brain separates the important from the unimportant, is one of the many unanswered questions. Homeostatic regulation during sleep is probably the price paid for the plasticity of the brain, which strengthens synaptic connections during waking phases. It is a fundamental process that emerged in the course of evolution and is common throughout the animal kingdom.