bird brains

Zebra finches, native to the Australian desert, are opportunistic breeders that take advantage of a wet spell to quickly hatch their young. The bird is also common in pet stores -- and biology labs Photos by Nigel Mann.
Finally, support for dozing in class!
23 DEC 1998. Does snoozing make you smarter? Could 40 winks be worth 40 IQ points? For jumpers-to-conclusions, that's one implication of work coming out of some bird cages down at the University of Chicago.

Naturally it's not quite that simple. As you may have guessed, the studies concern songbirds, not people. And although they may point to how learning gets consolidated during sleep, they don't prove any increased learning whatsoever.

But they do show that a brain structure associated with singing became more responsive when the sleeping birds heard their own song.

It's curious. Normally, sleeping birds neither sing nor hear their song. And while birds sometimes show the rapid eye movement that signals human dreaming, these birds weren't dreaming about singing, or anything else, since their eyes were still.

This is not a dream.
Normally, sensory responsiveness falls, not rises, during sleep, says Daniel Margoliash, associate professor of whole-animal biology at the University of Chicago and an author of a new report on bird song and the brain in Science.

Using tiny devices that record the firing of a single neuron, Margoliash has found odd behavior in a structure called the robustus archistriatalis (RA). The RA, and another structure called the HVc (which stands for simply HVc), play vital roles in the nerve pathway that hears and produces birdsong. The HVc puts out bursts of activity whether a waking bird is singing or listening to its song.

Similarly, when an awake bird sings, the RA emits bursts of signals to control the muscles of the vocal organ. Yet even though it's a motor and sensory nucleus, it shuts off in sensory mode -- when a bird hears a recording of its song, its RA simply emits a monotonous beep.

And yet the RA does respond to the bird's song -- when the bird is under anesthesia!

The startle factor
To investigate what he calls this "surprising" result, Margoliash and graduate student Amish Dave played digital recordings of a bird's own song to sleeping zebra finches. The sounds caused the RA to begin firing in bursts, indicating that it was doing some neural processing.

But why would the neuron gain sensory responsiveness when the animal was asleep?

finchThe obvious conclusion is that the RA was attuned to hearing the bird's own song, but, as one former president famously intoned, "That would be wrong." That conclusion makes no sense, Margoliash points out, since birds don't normally hear their own song while snoozing.

Rather than showing that the RA is "listening" while the animal sleeps, he thinks the study demonstrates that the brain changes as the animal slumbers. "We have learned about how the system is rewired when the animal is asleep. They have access to certain types of information at night -- from higher centers in the brain -- that they don't have access to during the day." In other words, Margoliash hypothesizes that at night the brain seems to replay "tapes" of its songs for the RA nucleus to process.

Please pass the meaning
If it doesn't prove that birds like to hear themselves sing in their sleep, what's the significance of the discovery? Perhaps to hint at the biological role of sleep, which Margoliash calls a "ubiquitous behavior that is one of the least well understood."

This study -- and other evidence -- indicate that sleep is a time for consolidating or "stabilizing" the day's lessons, observations and motor tasks. To put it in highly technical terms, during sleep, the mass of information acquired during the day "sinks in" to the brain during the right. "There are reasons to wonder whether ... trial-and-error learning can occur in rapid, on-line fashion" while an animal is awake, Margoliash says.

Even a bird, he adds, must make sure its song does not get rusty -- that its language does not degrade. And thus "replaying tapes" during the night might allow the RA to process the sounds and sing better in the morning.

And while the recent study might seem to justify the subliminal audiotapes that are sometimes hyped to improve learning, the take-home message is not that "Dr. Dan's Special Memory Tapes" will help you conjugate French verbs faster.

Instead, it's more proof that your mother was right. Get a good night's sleep so you'll remember yesterday's French class -- or maybe start singing like a zebra finch..

-- David Tenenbaum

The Why Files
Behavioral State Modulation of Auditory Activity in a Vocal Motor System, Amish Dave, Albert Yu and Daniel Margoliash, Science, 18 December, 1998, pp. 250-4.

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