3. Why do we sleep and dream?
We spend about a third of our lives sleeping. Why do we invest so much time in sleep? The most straightforward answer is that sleep is restorative, and that it replenishes the body’s energy stores. However, intense neural activity during rapid eye movement—or REM—sleep, the stage in which most dreams occur, suggests that there may be more to the story.
One theory, which by far has the largest body of evidence, is that sleep plays a critical role in learning and consolidating memories. It is probably why infants and toddlers need up to 14 hours of sleep a day, with half of it spent in REM sleep. In adults, dreams may also play a role in brain plasticity and learning, which is why sleep-deprived adults perform worse in memory tests and tasks.
