Jürgen Aschoff

Aschoff has published articles with both Pittendrigh and Serge Daan, the latter also a pivotal researcher in chronobiology. In his recent work, Daan has attempted to reconcile the idea of parametric entrainment to light proposed by Aschoff with the non-parametric model of entrainment proposed by Pittendrigh, and results from a 2008 paper from Daan's lab lend further evidence to Aschoff's model of parametric entrainment.

Aschoff's rule is related to the model of parametric entrainment, which assumes continuous phase changes. Aschoff and Pittendrigh approached the field with different models of how oscillators entrain, which resulted in different predictive models. Aschoff's parametric model states that entrainment occurs through gradual changes in the clock that adapt to a new light-dark cycle. Although this is no longer recognized as the correct model in the field, Serge Daan suggested in 1998 that Aschoff made qualitative contributions that provide valuable alternatives to inconsistencies in the current field.

At a dinner held in Aschoff's honor at the 1991 Gordon Conference on Chronobiology, Professor Till Roenneberg initiated the annual giving of the Aschoff's Rule prize to scientists who have advanced the field of chronobiology by presenting a plaque with a ruler on it to Professor Maroli K. Chandrashekera. Recipients choose the winner the following year and must follow two guidelines:

Aschoff was known as an excellent lecturer with a booming voice, and he took a special interest in creating a scientific community and encouraging young scientists. After his retirement in 1983 and return to Freiburg, Aschoff continued his scientific work in the form of further publications. Only the death of his wife Hilde broke his unusual vitality. Jürgen Aschoff died ten months after his wife in 1998, after a short illness at the age of 85 years.

In 1960, Aschoff coined the term Zeitgeber (from German for "time giver" or "synchronizer") to refer to external, environmental cues that synchronize an endogenous oscillator to the environmental cycle. To investigate the properties of natural endogenous oscillators, Aschoff exposed organisms to constant conditions without Zeitgeber cues (either constant light or constant darkness). The observations from this paper were formulated into the fundamental rules of biological clocks.

From the experiments communicated in 1960, Aschoff noted that under constant light conditions, the activity phase shortens in nocturnal organisms and lengthens in diurnal organisms. These trends were termed alpha compression and alpha expansion, respectively. In tribute to his mentor, Pittendrigh called this observation "Aschoff's Rule" in a 1960 publication, and the designation remains today.

In 1952, his mentor, Hermann Rein, was appointed director of the Max Planck Institute for Medical Research in Heidelberg. Rein brought Aschoff to the Institute as a collaborator to study circadian rhythms in humans, birds, and mice. Aschoff then moved to the Max Planck Institute for Behavioral Physiology in Andechs to work with Gustav Kramer, who showed time-compensated sun-compass navigation in birds, and Erich von Holst, who studied physiological oscillators. From 1967 to 1979, he was a director at the Max Planck Institute for Behavioral Physiology and an extraordinary professor in Munich. Aschoff was a scientific member and a member of the Kollegiums of the Max Planck Institute for Behavior Physiology, as well as senator of the Max Planck Society from 1972 to 1976.

Aschoff began his research on the physiology of thermoregulation by self-experimentation. He discovered that there was a 24-hour rhythm of variation in body temperature. After these experiments, he began investigating the basic mechanisms of circadian rhythm. In the 1950s, he met and began to collaborate with Erwin Bünning and Colin Pittendrigh. Aschoff began further experimentation studying the circadian rhythms of birds and mice under constant conditions. His results led to the conclusion that circadian oscillations of biological processes were innate and did not require prior exposure to a 24-hour day to be expressed.

Aschoff was born in Freiburg Im Breisgau as the fifth child of the pathologist Ludwig Aschoff (known for discovering the Aschoff-Tawara or atrioventricular node) and his wife Clara. He grew up in the liberal but morally strict world of Prussian academia. After the Abitur at a humanistic high school, he – according to his own statement "lacking a specific interest" – studied medicine at the University of Bonn, where he joined the Burschenschaft (fraternity) Alemannia Bonn. Aschoff’s scientific career began in 1938, when he moved to the University of Göttingen to study thermoregulation physiology with Hermann Rein. In 1944, he received the venia legendi. He then became a professor at the University of Göttingen in 1949.

Jürgen Walther Ludwig Aschoff (January 25, 1913 – October 12, 1998) was a German physician, biologist and behavioral physiologist. Together with Erwin Bünning and Colin Pittendrigh, he is considered to be a co-founder of the field of chronobiology.