Seasonal clock changing helps to synchronize human sleep/wake cycle across latitude

(University of Seville) In winter, the sleep/wake cycle is dominated by sunrise. Wake-up times tend to occur during the winter twilight regulated by the circadian photorecpetive mechanism. Bedtimes tend to occur eight hours earlier or sixteen hours later, in the middle of the winter night, regulated by the homeostatic mechanism that make us feel tired after a prolonged wake. This setting delays the sleep/wake cycle as latitude increases following the delay in the winter sunrise time.

from EurekAlert! - Social and Behavioral Science http://bit.ly/2VzjTyQ