A lecture extract on the science of sleep

Good morning, everyone. Last week we looked at how memories are formed. Today I want to turn to something we spend roughly a third of our lives doing, yet rarely think about: sleep.

Let's begin with a common misunderstanding. Many people imagine sleep as a single, steady state, rather like switching off a computer. In fact, the brain is remarkably busy at night. We move through cycles of roughly ninety minutes, passing from light sleep into deep sleep and then into what's known as rapid eye movement sleep, when most vivid dreaming happens.

So why does this matter for learning? In one well-known type of experiment, volunteers learn a list of word pairs in the evening. Half of them then sleep normally, while the other half stay awake. The next day, the group that slept typically remembers noticeably more.

The current explanation is that during deep sleep, the brain replays the day's experiences and moves important information into longer-term storage. Now, a word of caution. These studies are usually small, and they test fairly simple tasks, so I'd be careful about headlines claiming that a short nap will double your exam results. It won't.

The second idea I'd like you to take away concerns timing. Each of us has an internal clock that tells the body when to feel alert and when to feel sleepy. In teenagers, this clock tends to shift later, often by around two hours. So a sixteen-year-old who can't fall asleep before midnight isn't necessarily being lazy when they struggle to get up at seven.

Finally, you've probably heard that everyone needs exactly eight hours a night. Personally, I find that rule rather too neat. Most adults seem to need somewhere between seven and nine, and the right amount genuinely varies from person to person.

For next week, please read chapter four, and keep a simple diary of when you go to bed and when you wake up. We'll compare the results in the seminar.