As Far as We Know, Throughout Life, All Humans Sleep

Sleep is a truly universal behavior. The more genetically similar we are to a species, the more similar we sleep. Humans are known to have the most REM sleep out of the vertebrate species. Do animals sleep? The short answer is yes, but in different ways. Giraffes sleep for 1.9-2 hours a day in various 5 minutes increments, while Koalas sleep 16-18 hours a day. Dolphins, on the other hand, sleep with only one half of their brain at a time because they need to breath. Various other aquatic mammals are similar sleepers. The differences that are seen in sleep across species include; size, predator vs. pray, environment, cognitive ability, and diet. 

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Polysomnography is The Gold-Standard, But is Not Always Used

Do you think that individuals tend to overestimate or underestimate how much they sleep? People usually tend to overestimate their sleep by about 40 minutes to an hour. One way to avoid this estimation bias would be to monitor sleep with a Clinical-Grade Wristband known as an Actigraphy watch. The Actigraphy watch can tell total sleep time fairly accurately (within a minute of actual sleep time) with a battery life of up to a month. This watch is not statistically accurate at determining sleep onset latency and wake after sleep onset. Because of this, the watch is not beneficial in measuring various short periods of sleep and is not beneficial in trying to determine sleep disorders. If you are interested in diagnosing a potential sleep disorder, it is important for you to find a sleep lab so you can obtain a polysomnography.

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You Can Be Sleep Deprived Without Feeling Sleepy; You Can Feel Sleepy Without Being Sleep Deprived

Sleepiness does not increase linearly across the day; it fluctuates. Sleepiness fluctuates even more when an individual is sleep deprived. So, why do you feel sleepy? This can be caused by the following: variability in an individuals sleep schedule, a decrease in total sleep time, a biological need to sleep (it is time to sleep), what you eat, and waking during slow wave sleep (SWS) or REM. Every cell in the body has a biological clock. In fact, we have trillions of biological clocks in our body. The master clock is located at the edge of the hypothalamus in the brain and is known as the Superchiasmatic Nucleus. These biological clocks control our perception of sleepiness. There are two processes that underlie the biological bases of sleepiness; process 'S' and process 'C'. Process 'S' is homeostatic and is reflected by the amount of early SWS and Delta Spectral Power an individual attains. Napping decreases process 'S' and increases Delta Spectral Power. Process 'C' is an individuals biological clock and is reflected by the amount of REM sleep an individual attains. The classic way to measure circadian rhythm is with body temperature. This is because our lowest body temperature correlates with the onset of REM sleep. Process 'C' is also imperfectly correlated to how many hours there are in a day (~24 hours and 11 minutes).

 

Without Light and Other Zeitgebers, Our Clocks Unwind

Our Circadian Rhythm runs on a clock that is twenty-four hours and eleven minutes long. Just like plants, we need the sun in order to keep our biological clocks in pristine condition. Particles of light, known as photons, are a type of zeitgeber that keeps your circadian rhythm synced. Restricted access to light and other zeitgebers cause circadian desynchrony. Shift work can also cause forced circadian desynchrony. Traveling is a common cause of circadian misalignment. The invention of the plane allowed us to travel faster than our biological clocks could adapt to the time change. This unpleasant event is known as jet lag. Jet lag is more common when an individual travels east of their time zone because it is harder to adapt to a shorter day then a longer one. In the occurrence of jet lag, melatonin can be used to reset the circadian rhythm if taken just after sunset.

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It Is Simpler To Go To Sleep Than It Is To Wake Up

How does the brain go to sleep? There are two global systems; the Ventrolateral Pre-optic Area (VLPO), and the Ascending Reticular Activating System (ARAS). The VLPO is a group of neurons that is also referred to as the sleep on cells. Our sleep on cells produce diffuse GABA to inhibit arousal so that the individual can go to sleep. The VLPO is also located within sleep regulatory neuronal populations. After acquiring the appropriate amount of sleep the ARAS, or sleep off cells, begin to wake the body up from its slumber. Various neurotransmitters such as serotonin, dopamine, norepinephrine, acetylcholine, histamine, glutamate, and orexin/hypocretin are released in order to activate arousal.

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