Good morning, everyone. Today I'm going to talk about sleep, and I've divided the talk into three parts. First, I'll look at what the brain does while we sleep. Then I'll move on to what happens when we don't get enough sleep. And finally, I'll give you some practical advice for the exam season. So, let's start with the brain. Many people imagine that the brain simply switches off at night. In fact, that's not the case at all. During some stages of sleep, parts of the brain are almost as active as when we're awake. One of its most important jobs at night is sorting through the day's experiences and deciding which memories to keep. Right, that brings me to my second point: sleep loss. A common belief is that you can catch up on lost sleep at the weekend. Unfortunately, it isn't quite that simple. In several studies, people who had slept badly all week still made more mistakes than usual, even after two long nights in bed. Now, for the practical part. Most adults need somewhere between seven and nine hours a night. Some people insist that they're fine on five, but, and this is the important bit, very few of them really are. My main piece of advice is this: get up at the same time every day, even at weekends. That matters more than the time you go to bed. So, to sum up: sleep is an active process, lost sleep can't simply be saved up and paid back later, and a regular routine is your best friend. Oh, and two quick announcements before you go. This week's seminar is on Wednesday. Oh no, sorry, it's been moved to Thursday. Same time, same room. And the reading for next week is chapter four, not chapter three as it says in your handbook.