Vulnerability to sleep loss and to changes in sleep-wake schedule: Differentiation of the contributing role of individual characteristics of the homeostatic sleep drive and the circadian rhythm

People differ in their ability to cope with sleep loss and with a change in sleep schedule. However, knowledge on the specific properties of the sleep-wake mechanism that are most crucial in determining this tolerance is limited. Concerning the internal biological clock, that promotes sleep during night time and alertness during daytime, it has been shown that some people can be characterised as morning or evening types. In the first phase of the project we investigate additional aspects of the internal clock and how this relates to the vulnerability of changes in sleep duration and timing. By imposing consecutive 20 hour sleep-wake cycles instead of the normal 24 hour cycle, we will be able to measure the length of the internal cycle of individuals, which is often somewhat longer or shorter than 24 hours. Also, the speed of adaptation to a new external rhythm will be monitored and we will determine how stable this characteristic is over time in a given individual. In the second phase, we will examine the extent to which knowledge of these individual characteristics allows us to determine sleep quality and performance when sleep-wake behavior is disturbed, as in shift work.