Every autumn Linda Krentz felt her brain go on strike. “I just couldn ’t get going in the morning, ” she says. “I’d get depressed( 抑郁的) and gain 10 pounds every winter and lose them again in the spring. ” Then she read about seasonal emotional problem, a form of depression that occurs in autumn and winter, and she saw the light. Every morning now she turns on a special light box for half an hour and sits in front of it to trick her brain into thinking it’s still enjoying those long summer days. It seems to work. Krentz is not alone. Scientists estimate that 10 million Americans suffer from seasonal depression. There ’s never been final conclusion that treatment with very bright lights makes a difference. Until now, in three separate studies published last month, researchers report not only that light treatment works better than a placebo( 安慰剂) but that treatment is usually more effective in the early morning than in the evening. Why does light treatment work? No one really knows. “ Our research suggests it has something to do with the change of the body ’s internal( 内部的) clock, ” says psychiatrist Dr. Lewey. The body is programmed to start the day with sunrise, he explains, and this gets later as the days get shorter. But why such small changes make some people depressed and not others isa mystery. That hasn ’t stopped thousands of winter depressive patients from trying to heal