Rule #7 Sleep well, think well. • The brain is in a constant state of tension between cells and chemicals that try to put you to sleep and cells and chemicals that try to keep you awake. • The neurons of your brain show vigorous rhythmical activity when you’re asleep—perhaps replaying what you learned that day. • People vary in how much sleep they need and when they prefer to get it, but the biological drive for an afternoon nap is universal. • Loss of sleep hurts attention, executive function, working memory, mood, quantitative skills, logical reasoning, and even motor dexterity.

— Brain Rules by John Medina