A CAP that cools the brain could knock insomnia on the head. Doctors have devised a cap filled with tubes of chilled water that calms over-active minds, allowing the wearer to switch off and get a good nights sleep. In a study, insomniacs who wore the 'nightcap slept just as well as those without the condition. The US researchers say their gadget could provide a safe alternative to the sleeping tablets taken by millions of Britons and Americans night after night. The cap works by cooling a part of the brain called the pre-frontal cortex, which lies just below the forehead. MO