Evolution and function of sleep

This paper presents a brief historical review of the beginning of scientifi c studies on sleep research and evaluation of the electrophysiological basi cs. Subsequently, hypotheses are presented and discussed on phylogenesis an d function of NONREM- and REM-sleep as well as aspects of the regulation of energy conservation and temperature. Sleep may have first evolved out of r est/activity cycles. Later on, with the evolution of complex brains, sleep may also assume importance in development and maintenance of these structur es. Hence, special emphasis is placed on the influence of NONREM and REM sl eep on the reorganisation of neuronal networks.