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It has previously been found that matching a plant's circadian rhythm to its external environment's light and dark cycles has the potential to positively affect the plant. [65] Researchers came to this conclusion by performing experiments on three different varieties of Arabidopsis thaliana. One of these varieties had a normal 24-hour circadian cycle. [65] The other two varieties were mutated, one to have a circadian cycle of more than 27 hours, and one to have a shorter than normal circadian cycle of 20 hours. [65] a b Webb AA (November 2003). "The physiology of circadian rhythms in plants". The New Phytologist. 160 (2): 281–303. doi: 10.1046/j.1469-8137.2003.00895.x. JSTOR 1514280. PMID 33832173. S2CID 15688409. Hidaka, B. H. Depression as a disease of modernity: explanations for increasing prevalence. J. Affect Disord. 140, 205–214 (2012).Arushanyan, E. B. & Popov, A. V. Influence of damage to the suprachiasmatic nuclei of the hypothalamus of rats on the dynamics of short-period fluctuations of normal and abnormal behavior. Neurosci. Behav. Physiol. 25, 290–295 (1995). Disruption to rhythms usually has a negative effect. Many travelers have experienced the condition known as jet lag, with its associated symptoms of fatigue, disorientation and insomnia. [129] Albrecht, U., Sun, Z. S., Eichele, G. & Lee, C. C. A differential response of two putative mammalian circadian regulators, mper1 and mper2, to light. Cell 91, 1055–1064 (1997). After breakfast, the brain is primed for learning and problem solving in the first half of the day. In the afternoon, we feel healthy if we have accomplished enough work to feel satisfied with our efforts. Without a good night’s sleep, you have an overwhelming feeling that you are wasting the day. As time passes, muscle tone peaks. And as evening comes, body temperature drops, and the production of melatonin (sleep hormone) rises – and the body prepares for sleep. Pfeffer M, Korf HW, Wicht H (March 2018). "Synchronizing effects of melatonin on diurnal and circadian rhythms". General and Comparative Endocrinology. 258: 215–221. doi: 10.1016/j.ygcen.2017.05.013. PMID 28533170.