How sleep improves memory, performance

How sleep improves memory, performance

The Medicine Cabinet: Ask the Harvard Experts

By Howard LeWine, M.D.

Q: I don’t think I get enough quality sleep. I keep reading about how you need sleep to improve learning and memory. Why does that make a difference?

A: Scientists have long known that getting a good night’s sleep helps us learn and remember. The sleeping brain actively strengthens memories.

The sleeping brain lays down two kinds of memories. Declarative memory is memory for information, such as facts, dates and names. Procedural memory is what allows us to play a musical instrument, ride a bicycle or type on a keyboard.

Sleep scientists think that different parts of the sleep cycle influence these two types of memory. But there is a consistent pattern. You learn something new during the day. You strengthen what you have learned during a good night’s sleep. You remember and perform the task better in the morning.

There are two main kinds of sleep: rapid eye movement (REM) and non-REM (NREM). We dream most vividly during REM sleep. And the most vivid dreams of all occur at the end of the night.

In general, NREM sleep promotes declarative memories and REM sleep smooths out procedural memories. But the distinction is not clear-cut.

Sleep helps the most challenging memories. Experiments suggest that the sleeping brain works harder on the things that are most difficult for us to learn when we are awake.

Some propose that sleep promotes creativity and insight, not just straightforward procedural learning. In one study, subjects were given math puzzles to solve. A group that had slept between sessions did the problems slightly faster compared to a group that had not slept. More impressive, the subjects who slept were more likely to find a hidden solution to the puzzle that required insight, rather than a performance boost.

How much sleep do you need to make sure you maximize learning and memory? The best results seem to require eight or nine solid hours of sleep, including that last REM period.

(Howard LeWine, M.D., is an internist at Brigham and Women’s Hospital in Boston and assistant professor at Harvard Medical School. For additional consumer health information, please visit