Sleep plays an important role in how well our memory works, making it essential for learning. But as everyone who's ever stayed up late studying for an exam knows, you don't always get as much sleep as you need! The good news is that a study published in Proceedings of the National Academy of Sciences suggests that exercise can give your memory some protection when you haven't slept. Researchers worked with 53 participants aged 18 to 35 who came to a lab where they were kept awake for 30 hours non-stop. Then they were each put in one of three groups. One group did a 20-minute workout on exercise bikes, while a second group took a 90-minute nap. The remaining participants — the control group — did neither. Then all participants viewed 150 images while having the electrical activity in their brains recorded. They weren't told they'd be tested on the images, but three days later, they were brought back to the lab to do exactly that. The participants were shown a mix of new images and images they'd seen before, and asked which ones they remembered. Unsurprisingly, the participants who took a nap before first seeing the images did 23% better than the control group. But the exercise group did nearly as well, scoring 21% better on their memory test than the participants who didn't get to sleep or exercise. Interestingly, the brain activity recordings revealed that while naps and exercise help memory to a similar degree, they work in different ways. Napping seemed to help the brain recharge, making it easier to take in new information. Exercise, however, appeared to help the brain use its remaining resources more efficiently. The researchers said that exercise can't replace sleep. But these results suggest that it can help people at least function better when they haven't had enough rest.