What Is the Circadian Rhythm?
1. History
Androsthenes from the 4th century BC described diurnal leaf movements from a tamarind tree. In Chinese medical texts, the circadian or diurnal process was mentioned dating back to the 13th century. In 1729, a French scientist noted endogenous circadian oscillation in the 24-hour patterns of the leaf movements of Mimosa pudica despite being kept in total darkness.
By 1896, there was an observation where sleepiness increases and decreases in a 24-hour duration after prolonged sleep deprivation. In 1918, animals were found to be capable of maintaining a 24-hour pattern despite the absence of light and temperature cues. After several more discoveries throughout the years, in 1977, the term “circadian” was adopted. In 1994, the first mammalian circadian clock mutation was discovered in mice by Joseph Takahashi.
