The idea that sleep had a mentally restorative effect, sorting out and consolidating memories and ideas, was intellectually acceptable by the end of the nineteenth century. In ‘Peter and Wendy’,[2] J M Barrie wrote ‘It is the nightly custom of every good mother after her children are asleep to rummage in their minds and put things straight for next morning, repacking into their proper places the many articles that have wandered during the day. …When you wake in the morning, the naughtinesses and evil passions with which you went to bed have been folded up small and placed at the bottom of your mind; and on the top, beautifully aired, are spread out your prettier thoughts, ready for you to put on.’ The stories of Peter Pan take place in a mental world and contain many allusions to aspects of cognitive psychology, some of which predate their formal scientific investigation.[3]