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Why sleep?

Many ask, but few answer. We present two of science's most intriguing theories.

By | April 1, 2009

Sleep takes up around a third of our lives, and is an object of fascination during the other two thirds. "I dreamt that..." is surely among the top 10 conversation topics of all time.

Given this, it is surprising how little attention is paid to the anthropology of sleep. Intriguing (but too little) work has been done on sleep practices in nonindustrialized societies,1 and there has been some engaging speculation about sleep patterns;2 it all points to our Western conventions as being a behavioral outlier.

We condense our sleep into a single lengthy stint, in which any interruption is considered to be a pathology, while our forebears and preindustrialized societies enjoy segmented sleep. They also display a fuzzy "continuum of arousal...from...disengaged semialert, to somnolence or drowsing, to dozing, to napping,"1 while we tend to draw strict boundaries between sleep and wakefulness, and demand short transitions between the two (although my dad, and I'm sure many other dads, have given excellent demonstrations of all of these altered states for many years). Given our narrow viewpoint of normal, it's not surprising that "inadequate sleep is associated with unhealthy lifestyles and negatively impacts health and safety," a finding from the National Sleep Foundation's (NSF) "Sleep in America" 2009 poll (www.sleepfoundation.org).

We sleep alone from an early age and do everything possible to minimize sensory stimulation and isolate ourselves from the external environment. Perhaps this helps explain why the same poll found that "one-third of Americans are losing sleep over the state of the US economy and other personal financial concerns." Other cultures tend towards "multiple and multiage sleeping partners; frequent proximity of animals; embeddedness of sleep in ongoing social interaction; fluid bedtimes and wake times; use of nighttime for ritual, sociality, and information exchange; and relatively exposed sleeping locations that require fire maintenance and sustained vigilance." I feel that I'm missing out on the richness of the experience.

On first reading of the two features on sleep in this issue, I was skeptical of the use of rats and mice as good behavioral models of what I presumed to be the standard human sleep behavior. But the sociality, polyphasy, and gradations in alertness in rodents seem rather similar to that described in most humans, making extrapolations more comfortable.

In "Disappearing before dawn", freelance writer Kelly Rae Chi focuses on the crystallization of sensory information into memory. The traditional view is that memories are replayed during sleep, strengthening the appropriate circuitry. Researchers Chiara Cirelli and Giulio Tononi have turned this idea on its head, proposing instead that during sleep, synapses become weakened. The end result of both processes—the predominance of select circuits—is the same, but whether it is arrived at by the enhancement of particular synapses or the weakening of all but the strongest is a big deal.

The author of the second feature, Alan Pack, has demonstrated the possible ancient origins of sleep in the sleep-like state found in C. elegans. This is associated with molting,3 hinting that the original purpose of sleep may have been to allow for developmental changes. In "The Gears of the Sleep Clock", Pack proposes that one major function of sleep is the replenishment of resources—molecular, energetic, and structural—in the brain. These theories are not mutually exclusive; sleep serves multiple purposes. Likewise, it would seem that our various needs may be realized by multiple categories of sleep, such as that enjoyed by our forebears and less industrialized societies. It would be interesting to see more research on that.

References

1. C.M. Worthman and M. Melby, "Toward a comparative developmental ecology of human sleep." In: M.A. Carskadon, ed. Adolescent Sleep Patterns: Biological, Social, and Psychological Influences. New York: Cambridge University Press, pp. 69–117. 2. A. Roger Ekirch, At Day's Close: Night in Times Past. New York: W. W. Norton, 2006. 3. David M. Raizen et al., "Lethargus is a Caenorhabditis elegans sleep-like state," Nature 2008;451:569–72.
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Comments

Avatar of: Berry Muhl

Berry Muhl

Posts: 4

April 3, 2009

While you're bemoaning the loss of the "richness of experience" of sleeping with animals and children, take some time to consider the tradeoffs.\n\nI for one wouldn't trade in technological progress and security for it.\n

April 13, 2009

...because in my dreams I visit a whole different set of societies, hundreds of years/developed from this one. The complexities of each society are intricate, and (except for one thing) basic forms such as birth and death have changed so much as to be unrecognizable in this day & age.\n\nAlas. One thing NEVER seems to change; our propensity to make war and kill one another. As far as I know, I invented the 'mercenary' army--at least, in my SF (which I guess this is) the 'mercenaries' are totally unlike any others I've ever read about.\n\nI love my waking life too. In fact I'm pulled between the two worlds, and sometimes it seems as if this one is the ephemeral one...as if my dreams are 'as told to'. When bad things happen in my dreaming world, I try to hurry up and go back to this one. \n\nI've been told that if I write about my dreaming world, it'll either evolve or go away. I'll be damned if I write for publication however--there are features in the sexual realm that make these stories near unpublishable, (yes, like everything else, sex in some of these societies has certainly deepened) and if I try to write for online publication, I can't just say "This material is copyrighted" like I can for hardcopy written material, and have it be so. Damned if I give this stuff away...\n\nSo until online copyrights better evolve to protect original new material from a writer (and trust me, this is Original with a capital O, much to my surprise in finding it so), I'll just write for myself and a few trusted friends (who don't have computers and don't intend to purchase one). It sure beats the Y/A crap that passes for SF these days... So - as far as I'm concerned - that's why I sleep!\n\nThe interesting thing to me, is how my dream life impinges upon my waking one. I remember writing with my copyright declaration (one time use, North American copyright convention) and knowing that my stories (some of which were published) would be fully protected online. Seems that they have to be published in hard copy (magazines, etc) before they can be protected online.\n\nIt's simple, I'm told; all I have to do is to contact the Copyright Office and obtain hard copyrights for my material. But even back before online material was posted--even then, it took a long time to get a response from the copyright office--and that's the only way that I could be sure of getting an impregnable copyright for my material, these days. I sure wish I could do something besides contacting the copyright office--I've already tried that and they never answer. Probably backlogged from here to Kingdom Come, with writers who want to protect their material with an online copyright that's as impregnable as a hard-copy one used to be...\n\nThere. I've gone from 'why I (like to) sleep' to copyrighting the stories that come from my dream worlds. Yikes!\n\nBack to dreaming--I know some people who say they 'never dream'. Maybe it's so, I'm no expert on the subject. A friend of mine dreamed in serial episodes, akin to his real life. Another dreamed of all the bad things in his life. I can't say, looking at all that, that I have bad luck with my dreams! At the very least, they're fascinating, even to me.

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