Getting the ducks in a row: one-eyed sleep

You may know this already, but some birds and sea mammals sleep with one eye open and the other closed.  During this form of sleep, called “unihemispheric slow-wave sleep” (USWS), half of the brain (the one opposite the closed eye) gets a rest while the other half remains on duty, keeping the animals safe from predators or, if they’re marine, able to keep surfacing to breathe.

I’ve just learned of a ten-year-old study in Nature by Neils Rattenborg et al. looking at USWS in mallards, who often sleep in rows.  The researchers found that birds sleeping at the end of a row engaged in USWS 31% of the time, as opposed to only 12% for ducks in the middle.  Moreover, in “edge” birds, the  eye facing away from the center of the group was open 86% of the time, as opposed to only 52% — not different from random — for “inside” birds. EEG recordings showed that this eye-closing indicated sleep on the opposite side of the brain.

What is even more amazing is a fact documented in this wonderful Radiolab program on sleep rebroadcast yesterday (do listen to it if you have a free hour): the “edge” ducks occasionally turn themselves around 180 degrees. When they do this, the new outer eye is the one that remains open.

This behavior apparently allows both sides of the brain get some sleep! (We still don’t know why sleep is biologically essential, but it is: humans and rats deprived of sleep, for instance, eventually die.)

Another cute anecdote: Rattenborg also reports that he once saw a pet cockatiel sleeping next to a mirror:  “The mirror-side eye closed as if the reflection were a pal, and the other eye stayed open.”

The biological imperative of sleep remains one of the great mysteries of science.

______________

Rattenborg, N. C., S. L. Lima, and C. J. Amlander. 1999. Half-awake to the risk of predation. Nature 397:397-398.

15 Comments

  1. Duke York
    Posted December 27, 2009 at 7:02 am | Permalink

    During this form of sleep, called “unihemispheric slow-wave sleep” (USWS), half of the brain (the one opposite the open eye) gets a rest while the other half remains on duty…

    Wait… I don’t get it. The sleeping brain is connected to the open eye? The waking brain is attached to the closed eye? Do birds not have that hemispherical switch that mammals do?

    Cool column, tho.

    Duke

    • whyevolutionistrue
      Posted December 27, 2009 at 7:04 am | Permalink

      Sorry, a mistake, now corrected. Thanks.

    • Posted December 27, 2009 at 7:50 am | Permalink

      The left eye is “tied to” the right side of the brain and vice versa.

    • Torbjörn Larsson, OM
      Posted December 27, 2009 at 10:08 am | Permalink

      that hemispherical switch that mammals do

      Speaking of which, it is my half-remembered understanding that it isn’t a full visual field switch, but between a vertical symmetry axis. Checking Wikipedia:

      “Optic chiasm
      Main article: Optic chiasm

      The optic nerves from both eyes meet and cross at the optic chiasm,[11][12] at the base of the hypothalamus of the brain. At this point the information coming from both eyes is combined and then splits according to the visual field. The corresponding halves of the field of view (right and left) are sent to the left and right halves of the brain, respectively, to be processed. That is, the right side of primary visual cortex deals with the left half of the field of view from both eyes, and similarly for the left brain.[9] A small region in the center of the field of view is processed redundantly by both halves of the brain.

      Optic tract
      Main article: Optic tract

      Information from the right visual field (now on the left side of the brain) travels in the left optic tract. Information from the left visual field travels in the right optic tract. Each optic tract terminates in the lateral geniculate nucleus (LGN) in the thalamus.”

      [http://en.wikipedia.org/wiki/Visual_system]

      So that doesn’t seem to explain fully neither eye nor brain use when sleeping? If so, presumably there is something else than visual field processing controlling this, at least in mammals. Maybe it’s just contingency, as it seems to me either eye would do.

      Out of curiosity, which angular directions would the respective visual field halves cover in a duck anyway, assuming they have something like the mammal trait?

  2. NewEnglandBob
    Posted December 27, 2009 at 7:58 am | Permalink

    Too bad we can’t learn to do this form of sleep, although texting while driving might be a bit difficult this way since both hands are needed for texting.

  3. Sven DiMilo
    Posted December 27, 2009 at 8:57 am | Permalink

    humans and rats deprived of sleep, for instance, eventually die

    unlike the control groups?

  4. Reginald Selkirk
    Posted December 27, 2009 at 9:18 am | Permalink

    (We still don’t know why sleep is biologically essential, but it is: humans and rats deprived of sleep, for instance, eventually die.)

    The latest research shows that humans who are not deprived of sleep also die eventually.

  5. Torbjörn Larsson, OM
    Posted December 27, 2009 at 10:28 am | Permalink

    The biological imperative of sleep remains of the great mysteries of science.

    If it’s true as I remember it that it can be traced back to nematodes having some sort of less active state, it can AFAIU even be contingency.

    It could be due to the way the first animals with neurons solved how to construct neural controlled, or at least influenced, body clocks. Perhaps they benefited from or needed this quiescent state. It could easily happen to become “hardwired” as there likely was no need to be without it at the time.

    The latest research shows that humans who are not deprived of sleep also die eventually.

    In the discussion of that paper they propose to study if there is a casual relationship between life and death. All they have to do is to vary a parameter and observe the correlations. For example time – perhaps you don’t die if you aren’t born first?

    But for now suffice to say that such questions of life and death remain unobserved speculation.

    • Torbjörn Larsson, OM
      Posted December 27, 2009 at 10:37 am | Permalink

      D’oh! Didn’t mean to be so cavalier about life and death. I meant “causal” of course.

  6. aratina cage
    Posted December 27, 2009 at 10:32 am | Permalink

    Why do we need to sleep? Well obviously our souls get antsy dealing with the real world and need to have a little break in the spirit world, so they leave the control room for a bit each night. :P

    Seriously, this unihemispheric sleep dance that ducks do is really neat. People do some impressive sleep maneuvers too, like microsleep (and I thought that microsleep went against research suggesting that sleep deprivation could lead to death, as in you can’t not sleep unless you have the brain disease fatal familial insomnia).

  7. SaintStephen
    Posted December 27, 2009 at 11:54 am | Permalink

    Ducky!

    That’s amazing. Thanks for the usual dose of enlightenment, Professor Coyne!

    I had observed this odd behaviour many times myself, when forced to traipse through the swamps adjacent to golf course fairways, after a wayward drive. How fascinating to have it explained so clearly by an expert.

    And they say we aren’t robots… ;)

  8. Posted December 27, 2009 at 12:29 pm | Permalink

    Interesting – thanks.

  9. Voss
    Posted December 27, 2009 at 1:57 pm | Permalink

    Allow me, please, to express an opinion which has been percolating inside me for a few months.

    I JUST LOVE THIS STUFF!

    The diversity and complexity of biology is astounding. It moves me to tears (that is no exaggeration).

    Back when I was a Christian, I saw people react emotionally to the “spirit of God.” Their emotional ecstasy was something that I was never able to experience in a religious context. I was envious. To me, everything in that world seemed too drab to reflect reality. It was as though my fellow Christians were telling me how wonderful their black and white world was. I kept looking over my shoulder to catch glimpses of color outside of that world.

    Over the past year, evolution science has opened up a new life for me. I enrolled in college again as a biology major (at 57 years). I’m like a kid in a candy store.

    Jerry, if you ever feel that you are banging your head against a wall when a creationist misinterprets 99% of what you say, I hope you will remember that there are many of us who are just beginning to realize the beauty of the natural world. We need your help to do so.

    Thank you.

  10. Notagod
    Posted December 27, 2009 at 11:06 pm | Permalink

    Does the biological imperative of sleep extend to being alive but never fully awake, a christian could be a good example, would they be able to believe they will live forever because they never really wake up?


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