Dream A Little Dream
June 26, 2009 11:18 PM   Subscribe

Dreaming of Nonsense: The Evolutionary Enigma of Dream Content. Why on earth do our minds conjure up such ridiculous imagery, such inane thoughts, such spectacularly vivid and surreal landscapes, intense emotions—such narrative trash? posted by amyms (14 comments total) 6 users marked this as a favorite

In a 2006 study published in the journal Consciousness and Cognition, Zadra, Desjardins, and Marcotte performed a content analysis


I wonder if there is a single, specific reason for dreaming. There might be several advantages to doing it.
posted by Brandon Blatcher at 11:41 PM on June 26, 2009

I prefer the first explanation, that dream content is more-or-less screensavery nonsense just to keep the brain ticking over. I find the nonsense in dreams to be quite persistent even when lucid, suggesting that it doesn't have meaning. You can be both conscious of your dream, aware that it is nonsense, and still be acting through that in a credulous way. Even when you're aware enough to control a dream's content, some of the nonsense remains, and I think that because you're not fully aware the brain continues to fill in the rest with nonsense. Only once you've got to the stage of having real sensory input (like being aware of breathing/paralysis) does the dreamy stuff go away and is replaced with a processing of the outside world.

This is just my opinion, but the other three explanations don't fit my experience or make sense to me.
posted by Sova at 11:58 PM on June 26, 2009

I don't understand why dreaming must have a direct effect on evolution. Why can't it be a side-effect of some other, beneficial characteristic without any significant impact on overall fitness?
posted by Dr Dracator at 12:29 AM on June 27, 2009 [2 favorites]

I think dreams are pretty much just random. If they do help you work something out it's no more proof of their use than an interesting cloud pattern making you realise something. A combination of random brain firings that recall nuggets of previous experience and a brain trying its best to piece together a narrative from much sparser information than it gets when you're awake.

That's just from the my personal experience of dreams though. They all seem to be made up of chunks of sensations, like "the sensation of this person being a friend", or "the sensation of knowing something has gone wrong", just without any of the extra details like faces and explanations that you get in real life.
posted by lucidium at 2:16 AM on June 27, 2009 [1 favorite]

Interesting post, thanks.
posted by languagehat at 6:26 AM on June 27, 2009

The other night, I dreamt I went back to Maine (which I will be doing in a few days) and was walking through the woods barefoot on the way to a party, looked down, and realized the ground was covered in hypodermic needles.

Thing is, I wouldn't call that absurd imagery- I've actually found piles of trash containing hypos in the woods before. But as well, a friend I was pretty close to last summer used to be a junkie- and I've got reason to believe that since I've been gone she's gotten back on the wagon.

But that one was easy to explain. The night before I had a dream about going on a tour of Salzburg with Sarah Palin and Richard Nixon.
posted by dunkadunc at 6:34 AM on June 27, 2009

Every time I read this type of article I feel like a "dream foreigner", for lack of a better way to put it. For instance when they mention the question of why dreams have such a specific sensory profile of being so vividly visual and kinesthetic while comparatively impoverished in sound, smell and other sensory domains.

I've dreamt of playing music -- vividly. When I was a piano student it would sometimes happen that I would practice entire pieces in my dreams, then I'd wake up and be able to play them as I had in-dream. I could remember my fingering, pedalling, the pressure I'd used, the sound of the piano. I've dreamt of being sung to. Dreamt of the voice of someone I love and savoured all of its rich tones. Speaking of savouring, I've shared delicious meals with friends in dreams. I've dreamt of being in fields of wildflowers and being able to smell the damp earth and the riot of different flowers mingling (as I love to do in real life). I've dreamt of the tang of pine needles when you rub them between your fingers, and of the soft invigorating scent of lavender. All of my dreams have always been in color, with scent, sound and taste.

Sometimes the experience in itself is the meaning.
posted by fraula at 7:18 AM on June 27, 2009

I vote for the 'problem solving' theory.There is not a doubt in my mind that when my wife's cat is dreaming it is really dealing with the problem of developing new and ingenious ways of annoying me.
posted by notreally at 9:57 AM on June 27, 2009

I think the visual thing is just because vision is the only sense that is physically blocked when you sleep. You can still feel and hear and smell (and these things can wake you up), so those pathways aren't as idle.

From an evolutionary point of view, how expensive is thinking? Does it use more energy? Does it distract you from doing more useful things? We always read about how a big brain must be useful because of the great cost, but does that brain use more energy when playing a dense fugue than it does when thinking of more or less nothing?

Could dreaming be a way to do certain types of thinking on the cheap, with no distraction? I'm thinking particularly of learning-type activities, rehearsal and consolidation. The sort of thing we do when day-dreaming, but day-dreaming is more likely to get you run over (or eaten by a tiger).

Alternatively, if dreaming has no particular cost, it could just be completely random with no particular benefit. Or it could be detrimental, but an inevitable function of the way the brain has evolved.

Personally, I don't think dreaming is surreal enough to be a random artefact. There's some kind of narrative and process there- it's not random shapes noises, and colours, the words tend to form sentences. Maybe that's what randomness looks like at a particular level of consciousness, but that raises the question - why do we (all) appear to dream at that level?
posted by Wrinkled Stumpskin at 10:47 AM on June 27, 2009

The sleep episode of RadioLab is a pretty good summary of the purposes of sleep and gets into dreaming at the end.
posted by edbles at 12:28 PM on June 27, 2009

I didn't know about the costly signaling theory. It seems particularly unlikely. Dreams evolved because they're sexy?

You can imagine how someone came up with it. There's a general line of thought that leads scientists to posit handicapping and sexual selection as an evolutionary explanation for some trait. If an organism has some phenotypic trait that seems complex, then that trait probably costs the organism some resources (if not, it is a byproduct or spandrel). If it's costly, then it should have some function. If you can't find an obvious function, then maybe its function just is to be costly. You can run this hypothesis on pretty much any trait whatsoever.

But the explanation is only going to work if the trait is public. The opposite sex needs to see it in order to be attracted to it. Dreaming is about as private as you can get. Can mammals without language distinguish dreamers from non-dreamers? We don't even know which other animals dream.

This seems like a pretty obvious complaint though, so the neuroscientist advocating the theory probably addresses it. The books he's written and edited look really cool.
posted by painquale at 3:14 PM on June 27, 2009

Holy cow, check out the phylogeny of sleep database linked on that Boston University page! You can set various parameters to search the sleeping habits of over 127 million species!
posted by painquale at 3:24 PM on June 27, 2009 [3 favorites]

Hobson's activation-synthesis hypothesis. Full disclosure: my sleep research mentor did her post-doc with Hobson.

Dreaming is an odd state of mind because we only spend a third of our time there. The brain is a network, and it usually functions bidirectionally; sensory input comes in, informs our thoughts, and those thoughts become actions. Lather, rinse, repeat. But certain physical and mental processes are inhibited in sleep; physically, so we don't kill ourselves by actually walking off a cliff while we're dreaming about walking off a cliff. Mentally, we need to shut off the input to give the brain time to process what it's received. But this creates an interesting circumstance; the cerebral cortex, home of the "higher" functions, becomes silent. It goes from the dominant partner to a more reactive role. The older parts of the brain (one of my friends uses the term "lizard brain") takes over.

Normally, you control your computer (well, most of you) through your desktop GUI. You control the files by dragging them into folders, and so on. But imagine if you hooked the monitor's output to the defragmentation process. You'd see random bits of images and text as pieces of files are read in whatever order they happen to be written to disk. Just as information is scattered all over your hard drive's platters, the brain distributes information throughout its net. And as it processes all this information, the connection to the cerebral cortex is not severed—it's merely inhibited. So the cerebral cortex does what it does best with this seemingly random information (again, the way the information on your hard drive would appear random if you viewed the bits sequentially prior to a defrag); it constructs a narrative.

Everything we do is our narrative. Our brain constructs a story for everything we do. And so you have schema of what happens when you go to a restaurant; waiting to be seated, looking at the menu, arguing over the check. If you went to a nice restaurant and first saw the menu, then ordered, then got your food, and finally were seated, you might be somewhat uncomfortable. That's the schema for a cafeteria or a fast food joint, not a fancy restaurant. In a way, our consciousness is just a continuing narrative. And so when you become conscious during sleep (only during REM periods; you don't dream in "deep" or slow-wave sleep), you start to construct a narrative to the best of your ability from disparate neural impulses rising up from lower areas of the brain. Unfortunately, the part of the brain that helps you persevere and persist on thoughts (forebrain, IIRC; the part Phineas Gage got spiked through) is one of the newest brain structures and also one of the most inhibited (I think there's a relation, but that's just IMHO) during REM. So where you are, what you're doing, and even who you are shifts in a way that's sometimes uncomfortably fluid.

Fun fact: Have you ever noticed that almost all dream accounts start with the person describing where they were? "I was in a..." or "We were at a..." and the like. That's because the hippocampus is very active in REM sleep. In addition to playing an important part in formation of memories, it also handles spatial relation, navigation, and place.

So is there anything to dream interpretation? Yes, in the sense that things that you are thinking about and feeling currently inform the filters through which the dream narrative is constructed. Things your conscious mind may not feel comfortable with are let loose when your brain's inhibition centers are themselves inhibited. Dreams are a sort of mirror. The mirror itself doesn't tell us anything; it's just a neat optical phenomenon. The really telling bit is what we see in the mirror; it's in our evaluation and judgement that the real story is told.
posted by Eideteker at 1:01 AM on June 28, 2009 [2 favorites]

Not everything that a biological system does conveys an evolutionary advantage. To suggest that would imply that humans are perfectly adapted to our environment, which is pretty far from the truth. The slightest change in temperature, atmospheric gas concentration, radiation level, etc. and we're in trouble.
posted by WhySharksMatter at 9:13 AM on June 28, 2009

« Older Pastor Urges His Flock to Bring Guns to Church   |   Giant pebbles from outer space Newer »

This thread has been archived and is closed to new comments