The Frontal Cortex

Why We Dream

Over the weekend, I had a little essay in the Times on some new research on why dream at night.

When I can’t sleep, I think about what I’m missing. I glance over at my wife and watch her eyelids flutter. I listen to the steady rhythm of her breath. I wonder if she’s dreaming and, if so, what story she’s telling to herself to pass the time. (The mind is like a shark — it can’t ever stop swimming in thought.) And then my eyes return to the ceiling and I wonder what I would be dreaming about, if only I could fall asleep.

Why do we dream? As a chronic insomniac, I like to pretend that our dreams are meaningless narratives, a series of bad B-movies invented by the mind. I find solace in the theory that all those inexplicable plot twists are just random noise from the brain stem, an arbitrary montage of images and characters and anxieties. This suggests that I’m not missing anything when I lie awake at night — there are no insights to be wrung from our R.E.M. reveries.

While we’re fast asleep, the mind is sifting through the helter-skelter of the day, trying to figure out what we need to remember and what we can afford to forget.

Unfortunately for me, there’s increasing evidence that our dreams are not neural babble, but are instead layered with significance and substance. The narratives that seem so incomprehensible — why was I running through the airport in my underwear? — are actually careful distillations of experience, a regurgitation of all the new ideas and insights we encounter during the day.

Look, for instance, at the research of Matthew Wilson, a neuroscientist at the Picower Institute at M.I.T. In the early 1990′s, Wilson was recording neuron activity in the brains of rats as they navigated a difficult maze. (The machines translated the firing of brain cells into loud, staccato pops.) One day, he left the rats connected to the recording equipment after they completed the task. (Wilson was preoccupied with some data analysis.) Not surprisingly, the tired animals soon started to doze off, slipping into a well-deserved nap. And that’s when Wilson heard something extremely unexpected: although the rats were sound asleep, the sound produced by their brain activity was almost exactly the same as it was when they were running in the maze. The animals were dreaming of what they’d just done.

Wilson has spent the last few decades following up on this important discovery. In a 2001 paper published in Neuron, Wilson and Kenway Louie described the behavior of rats that had been trained to run on a circular track. As expected, running on the track generated a distinct pattern of neural firing in the rat hippocampus, a brain area essential for the formation of long-term memory. This is learning at its most fundamental: a flurry of electric cells, trying to make sense of a space.

Here’s where things get interesting: as before, Wilson kept the electrodes in place while the rats drifted off to sleep. (The sleep of rats is very human, and consists of distinct stages, including R.E.M.) The scientists examined 45 dreams and found that 20 of the dreams repeated the exact same patterns of brain activity exhibited while running in a circle. In fact, the correlation between the dream and the reality was so close that Wilson could predict the exact position of the rodent on the track while it was asleep. They were decoding the dream as it was being dreamt.

Why does the brain replay experience? Wilson and others argue that the dreaming rats are consolidating their new memories, embedding these fragile traces into the neural network. While we’re fast asleep, the mind is sifting through the helter-skelter of the day, trying to figure out what we need to remember and what we can afford to forget.

So why are dreams so much more than literal playbacks of the day just passed? Why the non-sequiturs, the long forgotten characters and the unexplained state of public undress? Wilson speculates that dreams are also an attempt to search for associations between seemingly unrelated experiences, which is why it’s so important for the controlling conscious self to disappear. What does this maze have to do with that maze? How can we use the lessons of today to get more food pellets tomorrow? This suggests that the strangeness of our nighttime narratives is actually an essential feature, as our memories are remixed and reshuffled, a mash-up tape made by the mind.

But wait: for the sleep- and dream-deprived, the news gets even worse. In recent years, scientists have discovered that R.E.M. sleep isn’t just essential for the formation of long-term memories: it might also be an essential component of creativity.

In a 2004 paper published in Nature, Jan Born, a neuroscientist at the University of Lübeck, described the following experiment: a group of students was given a tedious task that involved transforming a long list of number strings into a new set of number strings. This required the subjects to apply a painstaking set of algorithms. However, Born had designed the task so that there was an elegant shortcut, which could only be uncovered if the subjects saw the subtle links between the different number sets. When left to their own devices, less than 25 percent of people found the shortcut, even when given several hours to mull over the task. However, when Born allowed people to sleep between experimental trials, they suddenly became much more clever: 59 percent of all participants were able to find the shortcut. Born argues that deep sleep and dreaming “set the stage for the emergence of insight” by allowing us to mentally represent old ideas in new ways.

Or look at a recent paper published by Sara Mednick, a neuroscientist at the University of California, San Diego. She gave subjects a variety of remote-associate puzzles, which require subjects to find a word that’s associated with three other seemingly unrelated words. (Here’s a sample question: “broken,” “clear” and “eye.” The answer is “glass.”) Then, she instructed the subjects to take a nap. Interestingly, subjects who lapsed into R.E.M. during their nap solved 40 percent more puzzles than they did in the morning, before their brief sleep. (Subjects who quietly rested without sleeping or took a nap without R.E.M. showed a slight decrease in performance.) According to Mednick, the dramatic improvement in creativity is due to the fact that R.E.M. “primes associative networks,” allowing us to integrate new information into our problem-solving approach.

While Freud would certainly celebrate this research — as he predicted, dreams have “a psychological structure … which may be assigned to a specific place in the psychic activities of the waking state” — it’s worth pointing out that the stories we invent while sleeping are much more practical than he imagined. For the most part, they don’t reflect the unleashed id, full of unfulfilled sexual desires. Instead, we dream about what we think about: the mazes and mysteries of everyday life.

All this knowledge about the important roles dreams play in our waking lives is fascinating. But it doesn’t make me feel better about my insomnia. Obviously, my old consolation — dreams are nothing but useless melodramas — is clearly false. And though I eventually do fall asleep, lapsing into what I imagine is a rushed state of R.E.M., I can’t help but be jealous of my wife’s twitching eyelids at 2 a.m. She is busy remembering, processing, refreshing –and I am merely awake.

If you’d like a contrarian take on this dreaming research, be sure to check out Jerry Siegel’s 2001 take on the REM-sleep memory consolidation hypothesis. A century after Freud, it’s clear that our sleepy dreams remain mostly a mystery.

Comments

  1. #1 royniles
    March 22, 2010

    “-and I am merely awake.” Unless you’re merely dreaming that you’re still awake.

    But seriously, a good post that didn’t need some little O. Henry twist at the end to make it so.

  2. #2 elias
    March 22, 2010

    It’s worth noting that Freud’s dreams probably were full of unfulfilled sexual desires, because those were the everyday mysteries he thought about. : )

  3. #3 emily
    March 22, 2010

    more support for dreaming as memory consolidation: in jill bolte taylor’s “a stroke of insight,” taylor mentions that for years after her stroke she didn’t’t dream in the bizarre narrative sequences most of do, but in rem, probably like the mice, was more directly repeating whatever task she had been relearning to do.

  4. #4 6EQUJ5
    March 22, 2010

    At a former job I occasionally had to work 40-hour days (40 hours from waking until I next got to bed). After you’ve been working more than 24 hours straight, visual acuity starts coarsening, and whatever you look at begins getting grainy, a feature most easily seen in low light, as just before dawn.

    An hour of sleep is enough to restore eyesight almost to normal, so, having worked in engineering, I naturally wonder if dreaming isn’t a way for the brain to calibrate vision to get all the adjustments in order. As for consolidating learning, when doesn’t something have more than one function?

  5. #5 emilie
    March 22, 2010

    I’ve been wondering a lot about my dreams lately–they’ve been extremely vibrant in color and full of strange symbols (for example, dogs with human qualities, despite not being around dogs). It’s fascinating that the mind clings to these tiny little details from the day and blows them up in our dreams, assigning them emotional significance and dropping hints for us to analyze.

  6. #6 OftenWrongTed
    March 22, 2010

    From Henry David Thoreau:
    “I put a piece of paper under my pillow,
    and whe I could not sleep I wrote in
    the dark.”

  7. #7 OftenWrongTed
    March 22, 2010

    Sorry, sailboat lurched, it should be when instead of whe

  8. #8 Katherine
    March 22, 2010

    @6EQUJ5 #4: Or it could just be that your eye muscles need rest too. Ever tried using any other muscle for long periods of time?

  9. #9 edSanDiego
    March 22, 2010

    The subject of sleep is such a perfect match for a blog about the Cortex.

    During REM, the brain empties the cortex of all the new experiences and the repeated experiences it has taken in during the day (or if you sleep in the afternoon, the learnings in the hours since you last woke). There are various software programs that do the same for your computer hard drive – defragmentation or cleaning up and reorganizing data to make it easier to access next time around. When you wake up you have a clean(ish) cortex. The stored data is re-called as needed when associations take place through the day (or the amygdala takes over when you have to act on impulse or emotion because the cortex isn’t up to speed on an issue that was discussed a few years back).

    This is why taking sleeping pills is never a good idea. The pills help you to sleep, but a big point of sleep is to create connections and map the connections but all the pills do is knock you out. It also points to why getting enough sleep is important for new learnings – the cortex needs to be empty for the next day or the whole thing turns into minestrone soup when you really need something a little smoother and lighter.

    What would be interesting to investigate is whether the 90 minute or so REM cycles actually link to data being lodged in different parts of the brain during different cycles.

    Sleep is common to nearly every living organism. The fact is has survived through evolution in all species is testament that it is an essential part of life. We underestimate sleep and the amount of research that goes into it. We shouldn’t.

  10. #10 Jane Rubinsky
    March 22, 2010

    Sometimes I have absolutely no awareness of even having had a dream until I encounter something the next day and stop in my tracks with the sudden, startling awareness of having dreamt about it the previous night; though I can’t recall the dream itself, I know it has affected my feelings. Harvard researcher Dr. J. Allan Hobson’s argument that the main function of REM sleep and dreaming is to warm up the brain’s circuits and prepare us for the encounters & emotions of waking makes complete sense. A New York Times article on Nov. 9 by Benedict Carey quoted Hobson: “’It helps explain a lot of things, like why people forget so many dreams,’ Dr. Hobson said in an interview. ‘It’s like jogging; the body doesn’t remember every step, but it knows it has exercised. It has been tuned up. It’s the same idea here: dreams are tuning the mind for conscious awareness.’” Exactly!

  11. #11 Kevin Vogelsang
    March 22, 2010

    It’s interesting that so many extremely creative people tend to have the most sleeping issues. Anyone seen any research on this? There are a lot of creativity studies, unfortunately objectively defining creativity seems to be beyond us still, which makes them difficult to interpret accurately.

    I guess it’s a good thing I don’t sleep all that well. I’m already thoroughly bothered by the ideas I already have.

  12. #12 Scott Yates
    March 22, 2010

    I’m starting to worry about you!

    Have you tried listening to the BBC? I’ve found that works for my insomnia. Anything more boring and my mind would start racing. Any thing more interesting and I’d stay awake to listen. The BBC, with all their reports about NGOs and high commissions, seemed to do the trick.

    I hope that helps, I want you to sleep more!

  13. #13 Gabriel Ramos
    March 23, 2010

    Perhaps just a nuisance, but Wilson was not “decoding” the rat’s dream, as he was never able to measure the position of the rat during its dream. The prediction stands, but at this point it is untestable.

  14. #14 Jamie
    March 23, 2010

    A conclusion I gathered was a lifetime with insomnia could be a possible reason for poor school and learning abilities.

  15. #15 David Kincheloe
    March 23, 2010

    I’d like to hear why you dismiss Siegel’s criticisms so readily, and adopt the standard views of the pro- REM Memory Consolidation researchers. Perhaps the repetition functions to consolidate memory, but perhaps, instead, its basal neural activity with the meaning-overlay of repeated significant event/task/anxiety in order to “interpret” that basal activity, to account for it. We’re attibuting functional significance to a measure that’s not implied by the measure itself. I’d love your input…. Cheers. David

  16. #16 David Miner
    March 23, 2010

    If I were to be tested on remote-associate puzzles, It’s likely I wouldn’t do well, but my waking hours are organized around making and analyzing them. Over the last few years, it seems I dream almost every night; I have had scary, nightmarish dreams, although I have never been able to recognize anyone in my dreams. I have come to look forward to sleeping and can fall asleep in minutes—a dramatic change for me. It helps, I’m sure, that my bed is mine, not for anything else but sleeping and dreaming, many dreams presumably of unfulfilled sexual desires, without angst.

  17. #17 Dick
    March 23, 2010

    I’m another BBC listener. The trouble is, the more interesting the segment, the more likely I am to fall asleep during it. I hardly ever dream anymore. Is it because I’m plugged in all night? I dream when I’m at the dark, quiet cabin with no radio. Is that a clue that I should unplug?

  18. #18 Jesse Brown
    March 24, 2010

    There’s a relevant new paper in Neuron on hippocampal replay in rats (during rest or sleep) after running on a track :
    http://dx.doi.org/10.1016/j.neuron.2010.01.034
    Perhaps the most interesting finding was that some of the brain activity during sleep was related to the construction of never-experienced but feasible novel sequences in the track. This work echoes the other experiments mentioned and puts the idea of sleep-related novelty association on firmer footing.

  19. #19 Zoasterboy
    March 24, 2010

    @Kevin Vogelsang (#11)

    I think this is a generalization, unless otherwise shown.

  20. #20 Greg McBride
    March 25, 2010

    I disagree with the suggestive use of thinking as an action that is based on” well, thinking”. When we sleep, I believe we see a more natural view of what happens when we are awake. When awake, cognitive choices are made, interfering with the “normal” process that is storing of information. Conscience leverages the natural process, to align the known with the new, to ensure good out come of choices. The known, being simply the most common stored or referenced information. The processes of the brain, are not much different between the species, from Plants, to bugs, to animals. We think, due to the process of storing, which in our brain types, allow for a more direct interface, between stored data, and choice. All living things make choices, the plant turns with the sun. Many see the plant tracking the sun as the mere normal reactive processes, that are “part” of the plants physiology…I agree, and suggest we are built the same way. Our senses are simply data gathering inputs, that feed our brains storage systems. In our advanced frontal lob, the association of data is more fully available for complex associations, which result in more direct, and successful choices. I suggest that the events monitored during sleep cycles, is simply the base algorithim in action for storing data, without the constant interuption of new info, even though, new info, could be derived as a result of the mix active during the sleep cycle. There is no cognitive choice involved in the storing, though this to can change if a strong desire to do so exists, but rather the base process, is merely subsiding the remaining most active nexus of data, and the natural merging of known to new, and the residual echos of strong choice actions, that lit up the various storage areas. This is one of the reasons we have the often odd associations flowing into our dreams. Simply dreaming of being in the public eye is an action that has elements of embarassment, which shares storage with our most common fears, such as being inappropriately dressed in that environmental visualization. We think, based on the successful building of our storage abilities.

  21. #21 Greg McBride
    March 25, 2010

    Gabriel and Jesse, Combining your comments, points to a way to test the rats position in the maze.
    Suggesting that they could detect variants of the rats travels in its dreams, would allow them to build a maze based on the variant. If the rat has pre-knolwedge of the new layout,
    it would go a long ways towards indicating a proof.

  22. #22 Tybo
    March 26, 2010

    Oddly, a lot of research has been suggesting that it is in fact slow-wave sleep that may more important for memory consolidation. Sharp wave ripples have been observed in the CA1 region of the hippocampus in mice, macaques, and humans (with epilepsy, of course), and found to increase with presenting novel tasks and training before sleep. A paper came out just last year showing that suppressing the sharp-wave ripples in mice impaired their ability to run through mazes they had done the previous day, too, suggesting that the population-bursts that result in the sharp wave ripples are a necessary component of consolidation.

  23. #23 Beth
    March 27, 2010

    I am also an insomniac. Like this writer, I am also often jealous of my husband’s complete relaxation–even his soft snore. I have done many a day’s work on –maybe–two hours of sleep. I have to agree with edsandiego’s take on sleeping pills. I have tried a few over the years–nearly every time a new one came out–but found that these were more like passing out than sleeping. Given the cost of the doctor and the cost of the prescription, I bet a cheap bottle of whiskey would have provided a similar result–not real sleep. I continue to follow all of the advise–no big meals, exercise, or action movies before bed. The BBC suggestion is new to me, and I will try it tonight. Please keep this blog and these comments going–at least I know that I am not the only one. Thanks.

  24. #24 Žarko Milićević
    March 30, 2010

    Has anyone done on human subjects what Wilson had done with rats? I would be very interested to hear what would they dream about.

  25. #25 Edward Stabe
    September 11, 2010

    Whenever were physically tired or exhausted we tend to sleep quickly. The common perception being that we don’t dream much when we’re physically exhausted. Is this true? But more importantly, in case its true does it point to dreaming being some kind of process by which the info we’ve gathered while being awake (‘cache memory’) is being transferred into some ‘permanent memory’ optimized by whatever is already present in the ‘permanent memory’ (hence the insight & illogical dreams which seem perfectly normal when we’re dreaming)

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