Johanna Meijer

Johanna H. Meijer (born 26 March 1959) is a Dutch scientist who has contributed significantly to the field of chronobiology. She is known for unraveling the mechanisms of seasonal adaptation by the biological clock and for pioneering studies of light and behavioral effects in nocturnal and diurnal species. Some of these studies also focused on the prevalent changes in brain cells and brain tissue. Notably, Meijer is the 2016 recipient of the Aschoff and Honma Prize, the most prestigious international prize in the field of circadian research. In addition to continuing to elucidate neuronal mechanisms of circadian clocks, Meijer's lab now studies the effects of clock disturbance on human health and biodiversity.

Academic career
Meijer attended Leiden University in the Netherlands, where she obtained her master’s degree (cum laude) in the Department of Biology, Physics, and Medicine. Meijer began her work on circadian rhythms alongside electrophysiologist Gerard Groos, who sadly passed away in 1985. Meijer continued building on Groos’ foundational work, allowing for translational research, and expanded electrophysiological techniques to in-vivo recordings. In 1989, she completed her PhD. in Medical Sciences (cum laude). She obtained a fellowship from the Dutch Royal Academy of Sciences and was appointed full Professor of Neurophysiology in 2007.

Meijer has advanced her research on circadian rhythms and chronobiology as a full Professor and Chair of the Neurophysiology Group at the Leiden University Medical Center in the Netherlands. Additionally, she served as a five year visiting professor in the Department of Ophthalmology at the University of Oxford in the United Kingdom.

Major discoveries

 * Identification of the mechanism for photoperiodic encoding by the central clock
 * Identification of glutamate neurotransmitter for entrainment to the external light-dark cycle and GABA neurotransmitter for entrainment within the central clock
 * Discovery of short wavelength photoreceptor role for photoentrainment
 * Identification of blue, green, and red light response in the central clock of humans by fMRI
 * Identification of clock response to physical activity

Research and achievements
Meijer made fundamental contributions to our understanding of the biological clock in the brain of mammals and how these respond to change in the cycle of light and darkness. Her initial interests were in biophysics, brain research, and the philosophy of science. Throughout her career, she continued to integrate these domains.

Her first work on circadian systems began with an analysis of the electrophysiological (neuronal) responsiveness of the central clock in the mammalian brain, the suprachiasmatic nucleus (SCN), to light. She showed that glutamate is the main transmitter between the eye nerve and the SCN, and that NMDA (the glutamate receptor) is the major receptor involved in entrainment to light. Meijer demonstrated that long and short photoperiods are encoded by a redistribution of temporal activity patterns of individual neurons. Hence, photoperiodic encoding is a tissue property, comparable with pattern recognition by the visual cortex.

In contrast, the ability to generate 24-hour patterns is a single-cell property (Nobel prize-winning work of Hall, Rosbash, and Young). This shows that distinct hierarchical levels are responsible for different properties in the circadian system, as a model for the brain. This view prompted Meijer to incorporate complexity theory in her analysis.

Meijer continued to analyze the properties of the SCN both from a cellular and an integrated network perspective. She discovered that behavioral activity has a direct influence on the electrical activity of clock cells and enhances the amplitude of the rhythm. She also identified a major role for a short wavelength photoreceptor (UV light) in synchronizing the clock of nocturnal mammals to the light-dark cycle. She was the first to establish the response of the SCN to different colors in humans using 7T fMRI and observed reactions to blue, green, and red light.

The elevated light sensitivity of the SCN in nocturnal animals prompted Meijer to investigate the effects of high nocturnal levels of light, termed 'light pollution'. This led to a series of both laboratory and field studies, as well as a nationwide program to reduce light emission at night to preserve biodiversity.

Other research lines include the effects of clock disturbances on human health, including aging, depression, ADHD, fragile X, and cancer-related fatigue, as well as research on small clock enhancing molecules. Complexity approaches are applied to further understand the mutual interaction between the clock, brain, and behavior, leading to the conclusion that a continuous two-way information flow underlies the function of both brain and behavior.

Awards and recognitions

 * 2021: Member of Academia Europaea
 * 2020: Dutch National Research Agenda Grant of 10.2 million euros– “BioClock Consortium”. www.bioclockconsortium.org
 * 2020: “Ambassador of the Night” Initiative of the Dutch Nature and Environment Federation.
 * 2019: European Advanced Research Grant of 2.2 million euros, ERC: “The circadian clock in day-active species: preserving our health in modern society”
 * 2016: Aschoff and Honma Prize in Biological Rhythm Research (International Selection Committee, chaired by Dr. Takao Kondo)
 * 2015: C.U Ariens Kappers Award from the Netherlands Society for the advancement of Sciences, Medicine, and surgery- 2015
 * 2015: Board member, National Research Agenda (NWO) Complexity cluster; successfully raised 19.5 million euros on Dutch Complexity Research
 * 2014–Present: Member of the Royal Dutch Society of Sciences.
 * 1999: ‘Best teacher’ award for the period 1994-1999 of the study “BioPharmaceutical Sciences” at Leiden University.
 * 1993: “Aschoff’s Rule, a prize for eminent contributions in Chronobiology supporting the interdisciplinary spirit of the field” from Prof. J. Hall (noble prize winner).
 * 1989: Fellowship of the Royal Dutch Academy of Sciences.