Dream songs

Last night I dreamed that our local mall had been converted into a giant used book store.  (Something I would entirely approve of.)  We were going to to go shopping ("we" being my wife, me, and our younger son, who lives in Houston but was apparently up for a visit) but we realized that a bunch of other family members were unexpectedly going to descend upon us, and for some reason we knew they were going to walk into our house without knocking, which our dogs would not appreciate, so we had to get home fast.  But while trying to get out of the mall we were hindered by a bunch of science-fiction cosplayers wearing silver body paint.

After that, it got kind of weird.

Dreams are a very peculiar thing, but they (and the REM sleep stage during which they occur) are ubiquitous in the brainier species of animals.  In fact, as I'm writing this, my puppy Jethro is curled up in his bed by my desk dreaming about something, because his paws are twitching and every once in a while he makes a very cute little "oof" noise.  But what would a puppy dream about?  Presumably the things that make up his waking life -- playing, chasing squirrels, swimming in our pond, eating his dinner.

You have to wonder if sometimes dogs, like humans, have weird dreams, and what they might make of them.

The function of dreaming is unknown, but what's certain is that it's necessary.  Suppress REM and dreaming, and the results are hallucinations and psychosis.  Aficionados of Star Trek: The Next Generation will no doubt remember the chilling scene in the episode "Night Terrors," where something is preventing the crew from experiencing REM sleep, and Dr. Crusher is in the makeshift morgue where the victims of a massacre are being examined -- and when she turns around, all the dead bodies are sitting up, still shrouded in their sheets.  She closes her eyes -- exhibiting far more bravery than I would have -- and says, "This is not real," and when she opens them, they're all lying back down again.

*shudder*

In any case, what brings up this topic today is far cheerier; a fascinating piece of research out of the University of Buenos Aires that looked at dreams in an animal we usually don't associate with them -- birds.  A team led by Gabriel Mindlin looked at a species of bird called the Great Kiskadee (Pitangus sulphuratus), a brightly-colored and vocal flycatcher found in much of Central and South America.  

Mindlin is one of the foremost experts in the physiology of bird song.  Birds have a unique apparatus called the syrinx that allows them to make some of the most complex vocalizations of any group of animals; not only can some (such as many wrens and thrushes) produce two or more tones at the same time, birds like parrots, mynahs, lyrebirds, and starlings are brilliant mimics and can imitate a variety of other sounds, including human speech.  (A lyrebird in a park in Australia learned to convincingly imitate a chainsaw, a car alarm, various cellphone ringtones, and a camera shutter.)

What Mindlin and his team did was to implant electrodes in the obliquus ventralis muscle, the main muscle birds use to control pitch and volume in vocalization, and also outfit some Great Kiskadees with devices to monitor their brain waves.  When the birds went into REM sleep, the researchers found that the OV muscle was contracting in exactly the way it does when the birds vocalize while awake.

The birds were singing silently in their sleep!

Singing in birds generally serves two purposes; mate attraction and territorial defense.  (As one of my AP Biology students put it, "they sing when they're mad or horny.")  It's more complicated than that -- science generally is -- but as a broad-brush explanation, it'll do.  Many species have different songs and calls for different purposes, each associated with a specific pattern of contractions and relaxation of the muscles in the syrinx.  Mindlin and his team used software capable of taking the muscle movements the electrodes detected and decoding them, determining what song the bird would have been producing if it was awake.  What they found was that the song their test subjects were dream-singing was one associated with marking out territories. 

"I felt great empathy imagining that solitary bird recreating a territorial dispute in its dream," Mindlin said.  "We have more in common with other species that we usually recognize."

So birds dream, and the content of their dreams is apparently -- just like Jethro -- taken from their own umwelt, the slice of sensory experience they engage with while they're awake.  (I wrote in more detail about the umwelt a while back, if you're curious.)  

On the other hand, how this accounts for my dream of silver-body-painted cosplayers in a mall filled with old books, I have no idea.

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