 We know that physical activity can have strong anti-depressant effects, but so far we actually don't have much of an idea about how physical exercise might work as a treatment. So I'm John Royzer from the UCL Institute of Cognitive Neuroscience, and I am the principal investigator of a new project funded by Welcome. In our study, participants will be undertaking the standard kinds of activities that people would do in a gym, and then in order to test whether the effects are really specific to aerobic exercise, we also have another group which is looking at stretching and relaxation. It's quite likely that physical activity will be really helpful for some people, and maybe not so helpful for others, by understanding the mechanisms better. Maybe we'll be able to persuade clinical commissioners and doctors themselves that physical activity is actually a worthwhile prescription.