Research Overview

Circadian rhythms have evolved as essential adaptations to the temporal structure of our environment, governed by cycles of day and night and by seasonal variations in light. Prof. Johanna H. Meijer investigates how the brain integrates these external cues with intrinsic cellular signals, revealing how the fourth dimension—time—is encoded within neural circuits. Her work explores how the central nervous system continuously merges environmental factors and internal biological information into a coherent temporal program.

At the heart of her research lies a unique and self-developed in vivo methodology, which allows for direct, long-term recordings of neuronal activity in the brain’s biological clock—the suprachiasmatic nucleus (SCN)—under naturalistic conditions. By combining in vivo brain measurements with behavioral readouts such as sleep and physical activity, she was the first to simultaneously quantify how internal clock mechanisms and external behaviors influence one another in real-time. This approach has offered a level of resolution and realism unmatched in the field.

Prof. Meijer is one of the very few researchers to incorporate concepts from complexity theory into chronobiology, enabling her to capture the dynamic, nonlinear interactions between sleep, light, and activity, and how these shape circadian function over time. Her work has revealed the critical role of both sleep and activity in modulating the SCN—findings that reshaped our understanding of the brain’s timing system. She also identified the neurotransmitters responsible for photic entrainment (glutamate, GABA) and the principle of seasonal encoding through phase coordination within the SCN. This refined the mechanistic picture of how the brain encodes and adjusts to time.

In addition to her pioneering research, Prof. Meijer founded the BioClock Consortium, a nationwide interdisciplinary research initiative in the Netherlands dedicated to investigating how circadian disruption impacts both human health and ecological systems. Through this platform, she mentors a growing number of PhD candidates and postdoctoral researchers, fostering a new generation of scientists committed to applying circadian insights to real-world societal and health challenges.

Her research does not just study the clock—it studies how the brain itself functions as a time integrator, continuously merging inputs from the world outside with cellular processes from within.

For her groundbreaking and integrative contributions to neuroscience and chronobiology, Prof. Meijer received the Aschoff and Honma Prize—the most prestigious international award in the field of biological rhythms.

Major discoveries

1. Identification of the mechanism for photoperiodic encoding by the central clock
2. Identification of glutamate neurotransmitter for entrainment to the external light-dark cycle and GABA neurotransmitter for entrainment within the central clock
3. Discovery of role for short wavelength photoreceptor in photoentrainment
4. Identification of blue, green, and red light response in the central clock of humans by fMRI
5. Identification of clock response to physical activity and sleep
6. Identification of differences in photoentrainment mechanisms between nocturnal and diurnal rodents

Contributions to circadian research

Prof. Johanna Meijer has made contributions to the field through her research on the effects of clock disturbances on human health, including aging, depression, ADHD, fragile X, and cancer-related fatigue. Additionally, she has conducted pioneering research on small molecules that enhance clock function. By applying complexity approaches, she has further developed our understanding of the mutual interactions between the clock, brain, and behavior.

Major recent publications

• Caputo R, Schoonderwoerd RA, Ramkisoensing A, Meijer JH. Physical activity stimulates clock neurons of the day-active rodent Arvicanthis ansorgei. Proc Natl Acad Sci  2025;122(21):e2424545122. doi:10.1073/pnas.2424545122. Epub 2025 May 19.
• van Beurden AW, Tersteeg MMH, Michel S, van Veldhoven JPD, IJzerman AP, Rohling JHT, Meijer JH (2024). Small-molecule CEM3 strengthens single-cell oscillators in the suprachiasmatic nucleus. FASEB J. 2024 Jan;38(1):e23348. doi: 10.1096/fj.202300597RR. PMID: 38084798.
• Schoonderwoerd RA, de Rover M, Janse JAM, Hirschler L, Willemse CR, Scholten L, Klop I, van Berloo S, van Osch MJP, Swaab DF, Meijer JH (2022). The photobiology of the human circadian clock. PNAS, Mar 29;119(13):e2118803119. doi: 10.1073/pnas.2118803119

Awards and recognitions (selected)

• 2023: Scholaster Academiae Franekerensis
• 2021: Member of Academia Europaea
• 2020: Dutch National Research Agenda Grant of 10.2 million euros– “BioClock Consortium”
• 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