Our circadian “pacemakers” are the suprachiasmatic nuclei. These are located in the brain (within the hypothalamus, to be precise), and these are synchronized with the amount of light in the day and the times of the day. To be sure: it is not identical for all people…this is due to genetic differences based upon your heredity and where your ancestors originated. These suprachiasmatic nuclei receive input from light-sensitive cells in your retinas that give you an almost-exactly 24-hour rhythm within your body.
SAD (Seasonal Affective Disorder)
This is an affliction comprised of successive or continuous episodes of depression brought about in the change of seasons (such as late Fall to early Winter, and then repeating again during the Spring-Summer change). One of the key findings associated with a study of this affliction is that SAD-sufferers happen to secrete more melatonin during nights of Fall and Winter. Melatonin is a hormone that greatly affects our sleep patterns.
Coupled with this is the fact that the daylight and daytime hours diminish greatly, bringing about a feeling of sluggishness and over-tired responses. This is natural. We live in an artificially-lit world of light bulbs and computer screens, with an excessive amount of noise during the course of the day. Centuries ago, the winter months were a time to live quietly from what was grown, harvested, and gathered during the warmer seasons.
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