ABSTRACT
With the invention of the first commercially practical incandescent lamp in 1879, Thomas Alva Edison revolutionized the way human beings live and work. The addition of light in factories has made shift work possible, allowing unprecedented levels of industrial productivity and economic competition. But working the night shift-times of day in which human sleep is normally concentrated-is very difficult for most individuals. Impaired alertness and performance during the night-shift contribute to accidents on the job and automobile accidents on the way home. Similar risks undermine the health and safety of persons suffering from jet lag, in which the circadian rhythm of alertness is temporarily out of phase with local time. Shift work and transmeridian travel are now central to the fabric of the industrialized world, and the risk to public health continues to mount. Unfortu nately, treatments for impaired alertness and functioning are limited. This is because the most fundamental mechanisms of sleep-wake regulation-the mech anisms responsible for circadian rhythms in alertness and the increased sleep tendency that results from extended wakefulness-remain poorly understood.
