London - Scientists said yesterday they had discovered the secret of a natural alarm clock which enables some people to wake up more or less when they want to. Researchers from Germany's Lubeck University said the expectation that sleep will end at a certain time triggers a marked increase in the concentration of a hormone, adrenocorticotropin, in the blood.
The scientists came to this conclusion after studying the sleep patterns of 15 young and healthy volunteers, they reported in the British scientific journal Nature.