SERGE DAAN (1940-2018)

Published in ESRS Newsletter March 2018


When he engaged in sleep research in the beginning of the 1980s, Serge Daan was already an accomplished chronobiologist. He had obtained his post-doctoral training from two pioneers in the field, Jürgen Aschoff and Colin Pittendrigh. After his Ph.D. work on hibernation at the University of Amsterdam he spent two years in Aschoff's lab at the Max-Planck Institute for Behavioral Physiology in Andechs. There he studied how circadian rhythms of birds and mammals are influenced by season and latitude. In Pittendrigh's lab at Stanford University he focused on the functional analysis of circadian pacemakers in nocturnal rodents. This work gave rise to a series of 5 highly-cited papers that became classics in chronobiology. One of the influential new concepts was the dual oscillator model with an evening oscillator linked to dusk and a morning oscillator linked to dawn. These two oscillators are usually coupled but under certain conditions ("splitting") they may become uncoupled. It was the modeling approach that aroused Serge's interest in sleep. In 1980 Aschoff organized a meeting on the vertebrate circadian system where I presented the first version of the two-process model of sleep regulation. Based on rodent data it showed how the interaction of a circadian process with a sleep-wake dependent process can account for various effects of sleep deprivation. Serge immediately recognized the implications of the model, and since I was in the process of gathering human sleep EEG data, we decided to join our forces to simulate human sleep. I published a qualitative version of the two-process model in 1982, and with Serge Daan and Domien Beersma we jointly published two years later an extended, quantitative version. The model triggered a close collaboration between Serge's group in Groningen and my group in Zurich. Thanks to a grant from the European Training Program in Brain and Behavior Research we could organize mutual visits, initially twice a year, to discuss and exchange results and plan further projects. The scope of common projects in sleep and chronobiology was quite large and included experimental work, modeling and clinical studies in biological psychiatry. This collaboration continued throughout the 1980s and 90s. Among the outstanding students from the Groningen lab who performed research in Zurich as a postdoc or as a doctoral student were Derk-Jan Dijk, Paul Franken and Tom Deboer. Anna Wirz-Justice, a chronobiologist from the University Basel, and Rudi van den Hoofdakker, head of Biological Psychiatry in Groningen, played an important role in investigating the implications of the model for sleep and sleep deprivation in depression. In Zurich Irene Tobler studied applications to animal sleep, and Peter Achermann elaborated the model and introduced novel methods of signal analysis.

Serge Daan was appointed as Professor of Behavioral Biology at the University of Groningen in 1996 and was awarded with the endowed Niko Tinbergen Chair in Behavioral Biology in 2003. He served as Dean of the Faculty of Mathematics and Natural Sciences. Among the many honors and awards the most prestigious one was the International Prize for Biology which he received from the Emperor of Japan.

Serge was not only a creative and dedicated scientist, but also an inspiring teacher and mentor. He was critical towards his own theories and concepts, and readily recognized their limitations. I valued his openness and generosity during our long-standing collaboration and friendship. When I proposed in 2013 to reappraise the two-process model and present the results in a symposium, Serge was enthusiastic. Together with Anna and Tom Deboer we spent many hours preparing our joint presentation for the ESRS Congress in Tallinn.

When I saw Serge a year ago in Groningen, he told me with his usual enthusiasm about his work on writing a biography of Jürgen Aschoff. He was already visibly marked by his illness. It is a testimony to his dedication and courage that he managed to see the book in print at the end of the last year, two months before he left us.

Alexander Borbély