person with PTSD will experience the same anxiety routinely, and often when the connection is far more tenuous -- whenever he sees mud, or a hole in the ground, for example, but perhaps too as he dozes off to sleep. A pharmaceutical treatment is close. Some time ago researchers discovered that if subjects took propranolol, a beta-blocker, within a few hours of a traumatic episode, it reduced the likelihood of their developing PTSD. This was a fascinating finding, but given the need to administer the drug so quickly, of limited practical use (unless soldiers carry a supply with them). More recent studies suggest that propranolol can assist even those who have suffered from PTSD for years. Memory specialists use this analogy to explain the drug's impact. Imagine that you order a book in a library. The book is collected from the stacks. If you read it by an open window with the sun streaming in, the book will be slightly bleached. When you return it, what is stored is a fainter copy. Propranolol operates as fierce bleaching sunlight. If subjects with PTSD are prompted to conjure up an unwelcome recurring memory while being injected with the drug then the memory is re-filed in the brain in a weakened state. Fewer nightmares, less anxiety: an effect similar, some think, to the way that the emotional impact of his child's birth may have metaphorically shone bright rays on Shen Tong's ghastly dreams. *** The first mouse completed its swim in eight seconds.