The focus of my research interest is on the circadian system, both in normal and in pathological conditions. The circadian system is the set of physiological and behavioral variables that vary systematically as a function of time of day. A central component of the circadian system is the circadian pacemaker or biological clock, which in mammals is located in the suprachiasmatic nuclei (SCN) of the hypothalamus. Apart from experimentation, in particular at the behavioral level of the system, I apply mathematical tools to integrate existing knowledge of processes to help understand mechanism and function of the circadian system. Major questions addressed are: What is the influence of light on the circadian pacemaker? Can we infer specific features of the construction of the circadian pacemaker from behavioral responses? How does the circadian pacemaker regulate sleep timing? What are the functions of sleep, of nonREM sleep and of REM sleep? How do these sleep states depend on previous activities? How do various aspects of behavior depend on previous sleep? Given that light is the most important stimulus to reset the circadian pacemaker, what is the impact of light on variables downstream of the circadian pacemaker? Given that a separate non-rod non-cone photoreceptor system provides light information to the circadian pacemaker, what is the influence of that photoreceptor system on downstream variables, such as alertness and performance? Are differences between circadian pacemakers causing the differences in behavioral patterns between morning type and evening type individuals? Are abnormalities in the circadian system causally related to depressive disorder?
