Purpose of Sleep 3

From the Economist (Sep 18th 2008)

A strange case raises the question of what sleep is for

No actually I don't think it does. A couple of Italian patients with some degenerative disease and weird sleep patterns may be interesting for medical research, but studying them doesn't tell us much about the purpose of normal sleep.

Let's try out a much simpler example. We observe that eyebrows deflect sweat from the forehead and help protect the eyes. We might reasonably infer that this effect is the purpose for our having eyebrows at all. Even if a few people don't have eyebrows, and perhaps have developed some other mechanism for keeping sweat from dripping into the eyes, that doesn't force us to change our opinion on the purpose of eyebrows.

There are lots of biological and psychological functions in the human mind-body system. Sometimes these functions are broken or don't work properly. In the works of Oliver Sacks, for example, we can read many anecdotes of patients who have adapted, sometimes in curious or heart-warming ways, to their broken systems. But even if a system doesn't always work properly, that doesn't mean we can't appreciate its proper purpose when it does work properly.

Maybe it is possible to be both awake and asleep at the same time, as researchers now speculate. But that is not challenging our notion of the purpose of sleep, it is challenging our notion of the very nature of sleep. Not the same question at all.

Purpose of Insomnia

Can insomnia be a means to an end?

In a discussion on sleepnet, two of the contributors say their insomnia arose out of, and forced them to deal with, deeper problems they were confronted with (bad relationships, stress).

"A bad night's sleep is not necessarily a prelude to a bad day; I often find the resulting dreamy, detached condition rather better for my work that the excess of energy I get when I sleep well." Bryan Appleyard, On Insomnia. Selena Dreamy adds "Once you've broken through the pain-barrier, everything falls into place. You are dreaming, dreaming, dreaming ... communing with the gods. It is something very, very special!"

"I'm not sure I would continue to be myself if I lost my insomnia" Bryan Appleyard, On Insomnia 2. Neil Forsyth adds "Sometimes a person's affliction is the only interesting thing about them."

Purpose of Sleep 2

It would seem that men and women experience sleep differently.

• Bed sharing 'drains men's brains' [BBC News, 20 July 2006]
• Women experience significantly more nightmares than men and have more emotional dreams [BBC News, 11 September 2008]
• Sweet smells foster sweet dreams [BBC News 22 September 2008]
  

Meanwhile, German researchers find that odour cues during slow-wave sleep prompt declarative memory consolidation [Science, 9 March 2007]

So perhaps sleep is affected by the smell of the partner. Researchers at Wheeling Jesuit University found that Jasmine's odour leads to more restful sleep, decreased anxiety and greater mental performance [Wheeling Jesuit University via Sense of Smell Institute]

The Sense of Smell Institute is funded by the Fragrance Industry. So perfume helps you to fulfil the purpose of sleep does it?

The Algebra of Purpose

POSIWID tells us something about the purpose of worms.

POSIWID tells us something about the purpose of sleep (for worms).

So what does POSIWID tell us about the purpose of worm-sleep? Can we combine simple explanations of purpose into a more complex story?

Purpose of Sleep

According to a simple applications of the POSIWID principle, we can understand the purpose of sleep by observing its effects.

• Sleep plays a crucial role in flagging and storing important memories (New York Times, Oct 2007 via Psych Central)
• Sleep appears to have a dramatic impact on the way the brain functions the next day (BBC News, July 2008)
  

Alternatively, we can understand the purpose of sleep by observing the effects of sleep deprivation.

• In drivers and workers it can lead to fatal accidents. In those under interrogation it can lead to confession. (Economist July 2006)
  
• Sleep Loss Challenges Emotional Control (Psych Central, Oct 2007)
• No sleep 'renders brain erratic' (BBC News, May 2008)
  

And yet hundreds of articles on sleep begin with some statement about the difficulty of understanding its purpose.

• Philosophers, neuroscientists and researchers have struggled with this seemingly simple question for centuries. (Psych Central)
• The real nature and purpose of sleep has long puzzled scientists. (Science Clarified)
• The purpose of sleep is not entirely understood. (Dr Spock)

So where are the difficulties? For a start, there are some patterns of human sleep that don't fit the simple explanations.

• Less sleep may cure tiredness (BBC News, July 2002)
  
• Life's too short to sleep? Blame the 'Thatcher' gene (TimesOnline, April 2005)
• Gene determines sleep demands (BBC News, March 2007)
  

Meanwhile sleep (or something akin to sleep) can be found in a wide range of organisms that don't have memories or emotions quite like ours.

• Round Worms Help Explain Purpose Of Sleep (RedOrbit, January 2008)

Biologists would have us believe that the purpose of sleep is coded into some genes, shared between humans and other species. In evolutionary terms, the phenomenon of sleep appears to predate the kinds of effect we started with. Maybe humans are a bit ratty and accident prone after a disturbed night, but worms aren't. So we shouldn't infer the purpose of sleep from human effects alone; if there is a good explanation for sleep, it isn't necessarily a human-centric one. POSIWID may still give us important clues, but we need to interpret them carefully.

At least POSIWID gives scientists reasonable hypotheses to explore. Sometimes the only apparent alternative is a heuristic explanation, but Bateson and his followers (Watzlawick, Keeney) thought such explanations were like the empty explanation mocked by Moliere - explaining sleep by the presence of something called The Dormitive Principle. Bobby Matherne attributes a similar critique of empty explanation to Rudolf Steiner.

Further resources

• Imagining Sleep - an interdisciplinary course on sleep and dream
• Presentation Zen - Garr Reynolds on the Need for Sleep