Serotonin is a hormonal neurotransmitter closely linked to many of the body's vital functions, including the sleeping cycle. Doctors have found that babies who die of SIDS tend to have significantly lower amounts of serotonin than babies who die of other causes. "If you have a baby who gets into a compromised situation and they are becoming hypoxic, there are some babies who are sleeping. But medical researchers now think they have cracked the secret of what causes babies to die of SIDS, an advance that could save hundreds of lives each year. A lack of serotonin is suspected to hamper a sleeping baby's ability to sigismond up when its safety is threatened by a lack of oxygen or some other health hazard, said Dr. Moon, a pediatrician, SIDS researcher and associate chief of the division of general pediatrics and community health at the Goldberg Center for Community Pediatric Health at Children's National Medical Center in Washington, D.C.

"We think a lot of it has to do with arousal, and how babies can ettore up when they are asleep," Moon said.