Suprachiasmatic Nucleus
The SCN demonstrates that timing is centrally controlled and coordinated across the entire system.
The suprachiasmatic nucleus (SCN) is a rice-grain-sized cluster of approximately 20,000 neurons located in the hypothalamus directly above the optic chiasm (hence 'supra-chiasmatic'). It serves as the master biological clock in mammals. In 1990, Michael Menaker's lab at Stanford demonstrated the SCN's primacy by transplanting an SCN from a mutant hamster with a 20-hour clock into a normal hamster with a 24-hour clock - the recipient completely adopted the donor's rhythm within days. Earlier work in 1972 by Moore & Eichler and Stephan & Zucker independently showed that destroying the SCN erases all circadian rhythms. The SCN controls hormone release (cortisol, melatonin, growth hormone), body temperature oscillations, and cognitive performance cycles. Individual SCN neurons have slightly different periods (23-25 hours) but synchronize through neurotransmitter signals to a collective ~24-hour rhythm.
Business Application of Suprachiasmatic Nucleus
The SCN demonstrates that timing is centrally controlled and coordinated across the entire system. Organizations need similar 'master clocks' - clear scheduling policies and protected time blocks - to synchronize diverse workers with different chronotypes.
Discovery
Michael Menaker (1990)
Transplant experiment proved SCN is both necessary and sufficient for circadian rhythms