Theatre is a profession notable for having no retirement age and, at 89, the director Peter Brook has brought to London another of the shows created by the troupe he set up in Paris after departing, Prospero-like, from the RSC, where he had staged a celebrated King Lear in 1962 and A Midsummer Night’s Dream in 1970.A 75-minute piece for three performers and two musicians, The Valley of Astonishment deals with the brain disorder synaesthesia, which causes some people to process information in the form of colour, images or taste. This facility has given a journalist called Sammy (Kathryn Hunter) an astonishing ability to remember figures and data by turning them into word pictures, which skill she parlays into a career as “memory woman” in a touring human circus.Sammy&rsqu