Rest is work, less is more
Ferris Jabr, one of my favourite science writers, has an intriguing longform article up at Scientific American: "Why your brain needs more downtime". In it he expertly guides you through a series of research that show why naps, vacations, meditation and other mental breaks unfill your cluttered brain and allow it to run optimally.
I highly suggest heading over and reading the full article; it's truly longform writing at its best. However, for those exceedingly pressed on time, here's the TL;DR.
While we lounge in the sun allowing our minds to wander, our brains are hard at work. Research over the last two decades have shown that as we rest, disparate regions of the brain activate in coordination in what is called the "default mode network" (DMN) - one of the five "resting-state networks" that scientists have discovered so far. DMN activity may represent a way of introspection as we build a narrative of ourselves and those around us; it seems to be more active in exceptionally creative people and may be the root of epiphanies that seemingly appear out of nowhere. Many studies have found that resting-state networks activate as we rest after learning a complex new task - visual memory, motor skill, or language -which may help us retain the memory better.
As we go through our day, our cognitive resources are gradually depleted; naps and breaks replenish these resources and build their volume. Naps sharpen concentration and improve memory in all types of tasks in all age groups, though length matters: 10min naps immediately boosts performance upon waking, 20-30min ones require half an hour to kick off the "grogginess". An hour walk in nature has similar memory-boosting benefits, as long as you stay away from city streets and noise. Vacations revitalize your body and mind with new experiences -unfortunately the effects in general fade away between 2-4 weeks.
We also build our attention span during downtime. Mindful meditation - focusing on your thoughts, emotions and the present -seems to improve concentration and memory and nurtures the psyche. Meditation profoundly changes the brain's physical structure and strengthens connections within brain networks, including the DMN. Frequent meditation sharpens one's attention regardless of age, such that your middle-aged parents may outperform you on attention tasks. It works -the key is sticking to it daily.
Several studies show that meditating 10 to 20min a day considerably improves working memory - the ability to hold information in mind while manipulating it towards a goal - in college students from multiple countries. Meditation also reversed stress-induced working memory decline in US marines. Considering that working memory is frequently used as a marker for human intelligence, these results are nothing to scoff at.
As I'm typing this, I'm in the 5th day of a break from lab work after a horrendous month-and-a-half stretch of ~14hr workdays that resulted in total burnout. I'm still not really "resting"; my days are filled with neuroscience-related readings, writings and life-related stuff. Like many others, I experience a sense of guilt at the mere thought of some time off. This article comes as a timely reminder: knowing you need a break is not enough - you actually need to do it.