Sleep may be thought of as down time for the body, but as we rest, the brain is still up and running. No, you can’t learn a foreign language while you snooze. But sleep does play a pivotal role in learning and development. The brain that went to sleep last night isn’t exactly the same as the one that woke up this morning. While scientists still aren't sure why we sleep, they have conducted extensive research on the impact of sleep on our waking lives. Here are seven areas where the science backs up the common-sense idea that a good night’s rest is not just good for you. It's essential.   

1. Sleep helps you learn. 

While we sleep, the brain isn’t just resting. It’s busy rearranging and connecting its neuron networks in different ways. This helps you make associations, recognize patterns, and recall information. That old adage about getting a good night’s rest before a big test isn’t just about feeling alert while you’re bubbling in the answers. People recall information better after they sleep, even if it’s just a daytime nap. For instance, one study of auditory memory found that after people trained themselves on a pitch memory task, they performed better after they slept compared to before they slept. 

Scientists suggest that as we sleep, memories are being consolidated and transferred to other parts of the brain. This could be one reason we dream. Lab rats, for example, have been found to run mazes in their dreams, just as they do during the day. 

Memory improvements after sleep may be even more dramatic in children than in adults. Maybe that’s why kids need so much sleep!

2. Sleep helps you remember.  

While you may not be conscious of it, you can hear and smell during your sleep. When you hear or smell something as you learn, and then are exposed to it again as you sleep, it improves recall once you awaken. In a 2007 study, volunteers learned the locations of picture cards in a game similar to “concentration.” While they learned, they smelled the scent of a rose. Those who were exposed to the odor again while they slept that night remembered 97 percent of the locations, compared to only 86 percent for the people who didn’t stop to smell the roses as they slept. 

The smell (or sound) might help reactivate memories of the day, improving the ability to recall that memory in the morning.

3. Sleep improves motor skills. 

Researchers at Brown University identified a specific brainwave that occurs during sleep that seems to be vital to learning motor tasks, like playing the piano. Multiple studies have shown that musicians’ performance improves when practicing a new melody is followed by sleep. Further studies have shown sleep to improve other skills that involve coordination, like walking a complicated route, or, in the case of one 1988 study, trampolining

4. Sleep can make you less prejudiced. 

In a recent study, researchers put a group of 40 white individuals through an anti-bias training to reduce implicit, unconscious prejudice against women and people of color. While they looked at images that paired women and black men with non-stereotypical descriptors (like women and science words), an auditory cue pinged. Those who heard the sound again while they slept showed further reduction in measures of bias when they woke up. The result lasted for at least a week. 

5. Sleep helps you speak a new language—if you’ve already put some time in.

Sleep’s memory-boosting affects do apply to language-learning, though you can’t learn brand-new words while you’re unconscious. When German-speaking students were assigned to learn Dutch words for the first time, those who heard the same words played back to them while they slept could remember the German translation of the words better than the group who had the words played back while they were still awake. 

6. Sleep helps you navigate. 

When people dream, they may work out problems relevant to their waking lives—including spatial problems. When almost 100 people were taught to navigate a virtual maze as part of Harvard Medical School research, some of them has maze-related dreams (though, in the way of dreams, they weren’t necessarily solving that particular maze). Those who did performed better on the virtual maze later that day—better than those who didn’t sleep, and better than those who slept but didn’t dream. Other studies also suggest that sleep improves accuracy in navigating mazes. 

7. Sleep improves your immune system. 

Even if you’re a healthy person, sleep boosts your immune system. Just like you need sleep to remember foreign language vocabulary, your immune system needs it to remember how to fight off infection. In a study of healthy men, sleeping after a hepatitis vaccination improved the body’s immune response, making the vaccine more potent. In another study, people who slept fewer than six hours a night were 11.5 times more likely to remain unprotected from hepatitis B after getting the vaccine compared to people who slept more than seven hours, because their immune systems didn’t create antibodies to fight the virus.