Why Do All Animals Need to and How Do They Sleep

An Independent Project by Monika Nemcova ’19
Part 1 of 4

Even though sleep theoretically comprises a third of one’s life, an educated layperson knows basically nothing about it. I personally got through almost twelve years of rigorous formal education without getting to know more than that sleep is healthy (but why is it healthy I couldn’t tell) and that its amount per night should approach the magical number eight. I have, like everyone else at Andover, experimentally determined that if one doesn’t get enough of sleep, the next day feels like personal hell. Somewhere at the corners of my brain hovered information that there are two kinds of sleep – REM (as in “rapid eye movement” – that is when dreaming happens and eyes move rapidly below the eyelids – hence the name) and NREM (“non-rapid eye movement” – the peaceful slumber we don’t remember). This spring, I have decided to end this ignorance of mine and do an IP on sleep to finally understand this elusive phenomenon, which probably influences our day-to-day lives more anybody thought. Because I think that it is important that people know more about sleep, I will post here the weekly summaries of my readings, so everyone could see it.

Even though humanity has slept from its very beginnings, the study of sleep by itself is a very young field. Sleep came to the attention of the scientists in the early twentieth century when Sigmund Freud put forth that dreams contained messages about one’s suppressed desires and that they are crucial in unlocking one’s unconsciousness. While his claim is now generally regarded as pseudoscience (because it is impossible to prove or disprove it), it foreshadowed the efforts of future scientists to understand sleep. The breakthrough came in 1950 when a British physicist Robert Lawson during a long train ride noticed that the eyes of sleeping people were twitching under their eyelids [1]. He then spent the rest of the ride observing the sleeping passengers and the frequency of the rapid eye movements. Later, he wrote about this unorthodox experiment in a short letter to Nature [2]. A researcher at the University of Chicago, Nathaniel Kleitman and his graduate student Eugene Aserinsky decided to verify and quantify Lawson’s observations. In 1953, they proposed a relationship between the rapid eye motility observed during the sleep and dreaming, setting thus the now widely-known distinction between REM and NREM sleep. When they awoke sleeping people in the middle of their REM cycle, the vast majority of them was able to recall the dream they had or at least knew they were dreaming. In contrast, when they awoke subjects in the NREM phase, the overwhelming majority of the people could not remember their dream. Kleitman and Aserinsky also measured the interval between the individual REM phases and concluded that “An eye movement period first appears about 3 hr after going to sleep, recurs 2 hr later, and then emerges at somewhat closer intervals a third or fourth time shortly prior to awakening.” [3] When our sleeping cycle ends with the REM phase, we are able to recall the last dream. Their research also showed one of the reasons why it is so important to have a night of uninterrupted long sleep, as opposed to a few hours at night and a handful of naps – the REM phase starts only after several hours of sleep. The REM phase is crucial for learning and memory consolidation (I will discuss why is it so at some later point) [4].

 

SleepCircle
Figure 1. Copied from https://sleepcouncil.org.uk/how-much-sleep-do-we-need/

 

However, even after more than half a century of study, some aspects of sleep remain a mystery. For example, no one is sure why sleep evolved in the first place. Sleep seems like an evolutionary disadvantage – a period of time when an individual is vulnerable to the attacks of predators and cannot look for food or potential mates. Yet all animals sleep one way or another and mammals have the same sleep patterns as we do, complete with the REM and NREM phases. There must be a definitive evolutionary advantage of sleeping.

 

SleepTheories
Figure 2. Copied from https://backyardbrains.com/experiments/sleep#prettyPhoto/1/

 

Some propose that animals have evolved to eliminate the time spent by running around and being vulnerable to predators. Asleep, they are hidden, quiet and thus better protected. However, the counterargument presents itself very readily here – the individuals are less likely to escape the predators while asleep. Another theory proposes that sleep evolved to conserve energy – while we sleep, our metabolism, body temperature, and caloric demand all decrease [1]. That is, by the way, the reason why we do not even notice that we regularly do not eat up to ten hours because of sleep. If we don’t go to sleep, the body demand energy as usual – everyone has probably experienced gnawing hunger around two in the morning while desperately trying to finish an essay. Sleep also might have evolved as a time when the body could repair itself [1]. Personally, I have noticed that when I don’t sleep enough, my skin roughens, I’m more prone to acne, and I get sick easily. An important topic for students is also the role of sleep for memory consolidation [1]. We probably cannot determine a single reason why sleeping evolved but we can be sure that now it serves several different important functions and when we do not get enough of it, the body suffers greatly. Next week, I will focus on the neurobiology of sleep.

 

References

[1] Mar’i, J. (n.d.). Experiment: Sleep. Retrieved March 25, 2019, from https://backyardbrains.com/experiments/sleep

[2] Lawson, R. (1950). Blinking and Sleep. Nature, 165, 81-82. Retrieved from https://backyardbrains.com/experiments/files/Lawson-first-REM-1950.pdf

[3]   Aserinsky, E., & Kleitman, N. (1953). Regularly Occurring Periods of Eye Motility, and Concomitant Phenomena, During Sleep. Science, 118(3062), 273-274. https://doi.org/10.1126/science.118.3062.273

[4] What is REM Sleep? (2016, December 1). Retrieved March 25, 2019, from https://www.nichd.nih.gov/health/topics/sleep/conditioninfo/rem-sleep

Author: MsAndersen

Administrative Assistant

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