In 1929 Hans Berger proposed, after extensive studies using an electroencephalogram, that the brain is always in "a state of considerable activity" even when people were sleeping or relaxing. In the mid 1990s, Marcus Raichle had demonstrated that the human brain is a glutton, constantly demanding 20 percent of all the energy the body produces and requiring only 5 to 10 percent more energy than usual when someone performs mentally demanding tasks e.g. solving calculus problems or reads a book. He also noticed that a particular set of scattered brain regions consistently became less active when someone concentrated on such mental challenge to be then reactivated when someone was letting their thoughts wander.
The default mode network (DMN) is a brain circuit that is active when people are daydreaming. Downtime is an opportunity for the brain to make sense of what it has recently learned, to surface unresolved tensions and to redirect its powers of reflection away from the external world toward itself. DMN is more active in especially creative people: the mind obliquely solves tough problems while daydreaming. With the right kind of distraction DMN may be able to integrate more information from a wide range of brain regions in more complex ways than when the brain is consciously working through a problem. During downtime the brain consolidates recently accumulated data, memorizing the most salient information, and essentially rehearses recently learned skills, imprinting them into its tissue. Memory depends on sleep.
Most people can engage in deliberate practice for only an hour without rest. Extremely talented people in many different disciplines rarely practice more than four hours each day on average. Many experts prefer to begin training early in the morning when mental and physical energy is readily available. Vacations revitalize the body and mind by distancing people from current tensions. Giving people the opportunity to get a good night’s sleep is better than forcing their brains to concentrate on a single task for hours at a time. Some researchers have proposed that people are also physiologically inclined to snooze during a 2 P.M. to 4 P.M. The brain prefers to toggle between sleep and wake more than once a day.
Naps sharpen concentration and improve the performance of both the sleep-deprived and the fully rested on all kinds of tasks. A five-minute nap barely increased alertness, for 20 or 30 minutes there's a half an hour or more for wear off sleep inertia before regaining full alertness. 10-minute naps immediately enhanced performance just as much as the longer naps without any grogginess.
Beyond renewing one's powers of concentration, downtime can in fact bulk up the muscle of attention. Meditation is not equivalent to zoning out or daydreaming, but many styles challenge people to sit in a quiet space, close their eyes and turn their attention away from the outside world toward their own minds. Mindfulness meditation, refers to a sustained focus on one’s thoughts, emotions and sensations in the present moment, it's about paying attention to whatever the mind does on its own, as opposed to directing one’s mind to accomplish this or that. Meditation strengthens connections between regions of DMN, it can help people learn to more effectively shift between the DMN and circuits that are most active when we are consciously fixated on a task. Over time expert meditators may develop a more intricately wrinkled cortex (the brain’s outer layer), which is necessary for many of our most sophisticated mental abilities, like abstract thought and introspection. Meditation appears to increase the volume and density of the hippocampus, a seahorse-shaped area of the brain that is absolutely crucial for memory; it thickens regions of the frontal cortex that we rely on to rein in our emotions; and it stymies the typical wilting of brain areas responsible for sustaining attention as we get older.