In September last year Donna Saunders, a 33-year-old woman from West Sus, held a pillow over her sleeping mother's face for 30 seconds before stopping as her mother struggled and called out for help. In June she was acquitted of attempted murder because the court accepted that she was sleepwalking and was thus unaware of her actions. This is not an isolated case. The British courts are faced with an upsurge of “I did it in my sleep” defenses for crimes from erous driving to murder. The problem that this presents to lawyers and sleep experts is the subject of a conference at the Royal Society of Medicine. To the outsider, such cases prompt skepticism. But the sleep specialists who provide expert testimony at these cases know that many people are capable of carrying out very uncharacteristic actions while asleep as a result of sleep disorders. Between 2 percent and 4 percent of s sleepwalk, and there is plenty of evidence that strange somnambulistic(梦游的)actions like walking through hotels naked and urinating in cupboards are extremely common. Sleepwalking is caused by a “wiring error” in the brain. If a sleeping person is disturbed, the primitive, instinctive parts of the brain spring into life but the conscious controlling part does not. It's more likely to happen if we have a family history of sleepwalking, or are tired or stressed or have been drinking. Dr Idzikowski, director of the Edinburgh Sleep Centre, has given evidence in about 30 court cases involving sleepwalking. “I do think it is being used more often as a defense, possibly because the media has made people more aware of it," he says. The upsurge could partly be because of English law. William Wilson, professor of Criminal Law at the University of London and a speaker at the conference, says that in English law only people who have made a conscious decision to commit a crime can be punished for it. Sleepwalking, therefore, makes a good defense, particularly since it is hard to disprove. A person who has convinced a court that he or she committed a crime while sleepwalking may, under English law, be found “not guilty by reason of insanity”(even though this has nothing to do with the medical idea of insanity). Until recently, this almost inevitably resulted in being detained in a psychiatric institution.