He received his PhD from the Faculty of Medicine at the University of Groningen in 1988, under supervision of the biologist Serge Daan, the physicist Domien Beersma and the psychiatrist Rutger van den Hoofdakker.
The focus of his research was on testing the predictions of the two-process model of sleep regulation as developed by Alexander Borbely (1982), Serge Daan and Domien Beersma (1984).
Dijk then conducted post-doctoral research at the Institute of Pharmacology at the University of Zurich with Alexander Borbely and was a Faculty Member at Harvard Medical School and an associated neuroscientist at the Brigham and Women's Hospital, Boston MA, working closely with Charles Czeisler.
[7] Dijk's research focusses on the regulation and function of sleep and its interaction with the circadian timing system in humans.
[9] Dijk researches how individual differences in preferred timing of sleep is related to the biological clock and genetic variations.