The afternoon nap has always been a controversial topic. Its opponents see it as the ultimate expression of laziness, while its proponents view it as a catalyst for creativity and productivity. The latter point to historical figures such as Aristotle, Albert Einstein and Leonardo da Vinci, who are said to have drawn energy from power naps, even though the term ‘power nap’ did not exist back then. They also cite countries where the siesta is considered part of the cultural heritage. Now, research backs them up as well. A new study shows that even short periods of sleep lead to measurable changes in the brain that subsequently make us more receptive.
The results suggest that napping puts the brain in a state that enables us to store new information more quickly.
To understand this, it helps to take a general look at the brain. The adult brain contains around 86 billion neurons, which is more than ten times the number of people on Earth. These neurons are interconnected in the brain like a fine-meshed network. Information constantly flows along these connections, known as synapses, in the form of electrical currents and neurotransmitters such as serotonin and dopamine. During the day, as we learn or experience new things, this network is constantly changing. Some connections become stronger and new ones form.
If you remember a conversation, it’s partly because the connections between neurons in certain regions of the brain have been strengthened. In research terms, this is known as neuroplasticity — the brain’s ability to constantly rewire itself. This enables us to learn a new language, master new motor skills or even change seemingly ingrained behaviours later in life.
In recent years, research has shown that neuroplasticity occurs in a rhythmic manner. As new stimuli flood the brain during the day, existing connections are strengthened and new ones are formed. This process requires considerable energy and space. However, both of these resources are limited. It’s as if you were scribbling more and more on a chalkboard until eventually there’s no more space left and it all becomes meaningless. Then, in the evening, we sit on the sofa with a heavy head.
At some point, you have to wipe away some of those scribbles. On the one hand, to make room. On the other hand, it’s to store what’s relevant. In the brain, this happens at night while we sleep. Past experiments have shown that unnecessary synapses are then broken down or shrink to maintain a balance. This process is known as synaptic homeostasis.
This raises the question of whether even a short nap can restore order to the brain. To investigate this, brain waves were measured using an EEG. Certain signals can be used to determine the overall strength of the synaptic network, i.e. how strongly the neurons are connected to one another. As expected, this network strength increased in participants who had been awake for longer. However, the measurements also showed that even a short period of sleep was enough to reduce network strength again.
This suggests that synapses reorganise themselves during a nap. In a subsequent experiment, the researchers attempted to stimulate the nerve cells in the participants’ cerebral cortex that control movements in the ball of the thumb, from outside the skull. They initially set the coil to a low intensity, gradually increasing it until movement of the thumb could be detected. The weaker the connections between the synapses, the more energy is required externally to stimulate the nerve cell and trigger a movement.
Indeed, for participants who had taken a nap, the coil had to be set to a higher intensity. Sleep had weakened their network strength by pruning unnecessary synapses.
Over the past few years, researchers have conducted a series of mouse experiments to determine the extent of neural remodelling that occurs during sleep, i.e. how many of the brain’s connections remain constant and how many change on a daily basis. This research is interesting because it reveals just how malleable the brain is on a daily basis. It suggests that we may be much more mentally flexible than many people realise. For example, one group demonstrated that the contact area between synapses was almost a fifth smaller after sleep than before. They also found that almost four out of five synapses in the studied brain regions shrank, while only one in five remained unchanged.
What has not yet been investigated is whether the changes in the brain measured after a nap actually improve participants’ performance. However, a number of review studies demonstrate this. These studies show that participants were more alert and cognitively capable after a nap. For instance, they were better able to remember number sequences or words, and they reacted more quickly to certain stimuli. These positive effects were measurable in a meta-analysis of all the participants studied. This held true regardless of age, and applied to both regular nappers and those not accustomed to doing so. According to a NASA study, even pilots perform better during the landing approach of a long-haul flight if they have napped beforehand.
There are no specific tips for the perfect nap, such as how long you should lie down for or when you should do it. Sleep requirements vary greatly from person to person. Some people need ten hours a day, while others manage on five. This is probably why it’s hard to find definitive advice, even in studies. In one such study, researchers examined different nap durations and concluded: ‘Even though there is no single best nap length, a 30-minute nap seems to offer the best compromise between practicality and benefit.’
