Abstract:
What is sleep? Sleep is a state of behavioral quiescence with reduced sensory responsiveness. From the simple cnidarian, jelly-fish to human beings, sleep has been found to be a conserved behavior in the metazoan world (Allada & Siegel, 2008). Across species, this behavior has been defined as homeostatically regulated episode of rest, usually restricted to a particular time of day. A homeostatic regulatory mechanism signifies that sleep loss, either in duration or intensity, is recovered via sleep rebound – a compensatory mechanism which allows enhancement of sleep quantity or quality, either before or during the next sleep episode. Other than the sleep homeostat, another physiological entity that determines sleep is the circadian clock (Latin, circa meaning approximately, diem meaning a day). The clock times this behavior in accordance to the ecological niche of the organism, such that predatory risks are minimized, and availability of food and potential mates maximized. Sleep is also easily reversible, albeit at a high stimulus intensity. This characteristic of increased arousal threshold differentiates sleep from behavioral rest (immobile wakefulness), while easy reversibility distinguishes it from anesthesia, coma and hibernation. Homeostatic control is another unique distinction, separating sleep from rest. Additionally, sleep is also associated with a species-specific posture, resting place and behavioral attributes like yawning and others (Campbell & Tobler, 1984).
