Humans AND THE DISRUPTION OF CIRCADIAN RHYTHM.

WHAT HAPPENS TO THE BODY, THE MIND AND THE BEHAVOUR OF HUMANS. First things first: what is the circadian rhythm?

(oops! here comes some medical science, just a little) • Circadian rhythms are the changes that follow a 24- hour cycle, responding primarily to light and darkness in an organism’s environment. • They are found in animals, plants and many microbes These rhythms can influence: • sleep-wake cycles • hormone release • body temperature The study of circadian rhythms is called CHRONOBIOLOGY • Circadian rhythms are important in determining human sleep patterns. • The body’s master clock, or the suprachiasmatic nucleus (SCN), controls the production of melatonin, a hormone that makes you sleepy. The SCN is a small group of brain cells located in the hypothalamus that: • controls the circadian cycles • influences many physiological and behavioral patterns occurring over a 24-hour period. THE EFFECT OF Light on circadian rhythms.

(now that we know what it looks like and why it is there, let’s see how it works with light) • Light exposure to the eyes is the strongest external factor for and individual to maintain its 24-hour circadian rhythm. The SCN receives information about light through the eyes. The retina of the eye contains photoreceptors: • rods for seeing at night • cones for distinguishing colors But the retina also contains specialized ganglion cells: • they are photosensitive • they project directly to the SCN, where they help this master circadian clock Circadian rhythm and sleep • The circadian rhythm falls and rises at different times of the day. A typical adult will experience the strongest desire to sleep: • in the pre-dawn hours (2 to 4 am) • in the early afternoon (1 to 3 pm) It may be slightly different depending on whether you are a morning or a night person. • When we have been awake for a long time, sleep-wake homeostasis tells us that the need for sleep is gathering, and staying awake becomes more difficult. The effects of the disruption of circadian rhythm When the circadian system changes due to artificial light, • mood, • learning • memory become impaired. This can be seen in • jet lag • shift work situations. • When melatonin secretion goes down, because of untimely light, alertness levels increase. • Disruption of circadian rhythm as a result of light also causes changes in metabolism. Except for light, what other factors disrupt the circadian rhythm. Although light is the strongest one, it is not the only factor acting on circadian rhythm.

• Exercise • Feeding schedules • Social Interaction • Stress • Pharmacology have shown similar effects. treatment Dark therapy before bedtime, where light is filtered out with eyewear, is considered an effective method to: • promote earlier production of melatonin • improve sleep A NEW FIELD: SCOTOBIOLOGY

(You can’t tell what on earth it means? Of course it is Greek.) Scotos=Darkness Most biological systems on the planet depend on: • Day and night change. • Seasonal changes of light patterns. Photobiology (phos=light): The study of the role of light for essential activities such as: • Sight • Photosynthesis Scotobiology: the biology of darkness. • It studies the effects of darkness on the behavior and metabolism of animals, plants and microbes. • It lays the foundation for understanding the importance of dark night skies for all biological species. • It studies the positive responses of biological systems to darkness and not merely the negative effects caused by the absence of light. The presence of uninterrupted periods of darkness and their alternation of light is just as important to biological behavior. Thank you

• US National Library of Health (www.ncbi.gov) • National Institute of Health (www.nih.gov) • www.health.com • www.livescience.com