# Johanna Meijer

Johanna H. Meijer (born 26 March 1959) is a Dutch scientist who has contributed to the field of chronobiology. She started a national wide program, involving eight Dutch universities to study the effects of clock disturbance on human health and biodiversity. Meijer is the 2016 recipient of the Aschoff and Honma Prize.

## Biography
### 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 died 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
* Cancer-related fatigue is caused by a dysfunctioning circadian clock

## Research and achievements

Her initial interests were in biophysics, brain research, and the philosophy of science. Throughout her career, she continued to work in these domains.
Her first work on circadian systems began with an analysis of the electrophysiological responsiveness of the mammalian clock, the suprachiasmatic nucleus (SCN), to light.She showed that glutamate is the main transmitter between the eye and the SCN, and that NMDA is the major receptor involved in entrainment to light. Furthermore, she showed that GABA transmits information within the SCN.
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. This is in contrast to the ability of single cells to generate 24-hour patterns (Nobel prize-winning work of Hall, Rosbash, and Young). Together, these findings illustrate that distinct hierarchical levels are responsible for different properties in the circadian system. This view prompted Meijer to incorporate complexity theory in her analysis.
In her investigations of retinal photoreceptors, mediating entrainment, Meijer showed that classicalphotoreceptors are sufficient for entrainment. She identified a major role for a short wavelength photoreceptor (UV light) in synchronizing the clock of nocturnal mammals to the light-dark cycle. Furthermore, she established the response of the SCN to different colors in humans using 7T fMRI and observed reactions to blue, green, and red light.
The significant role of light to the mammalian clock 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, (28 nominated for the Igg Nobel Prize) as well as a nationwide program to reduce light emission at night to preserve biodiversity.
Meijer discovered that next to light, behavioral activity has a direct influence on the electrical activity of clock cells.
Other research lines include the effects of clock disturbances of human health, including aging, depression, ADHD, 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 the mammalian clock 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 (Nobel prize winner).
* 1989: Fellowship of the Royal Dutch Academy of Sciences.