Birds and people may not have much in common, but we might share at least one experience: dreaming.
And songbirds dream of what they know best — singing.
“Dreaming is not a very scientific term,” says Daniel Margoliash, a biologist at the University of Chicago and principle investigator of the recent study in the journal Science. “But I think dreaming is a close description of what happens to the animal.”
Margoliash and the lead author, Amish Dave, a medical student at the University of Illinois, found that the brain cells of zebra finches fire in very similar patterns while the birds are sleeping and while they are singing. And there may be a reason why the zebra finches sing in their dreams — to help them remember their songs. Songs are critical for birds in attracting mates and marking territory.
Sleeping to Learn
Recent experiments in humans and rats have demonstrated a strong correlation between learning and sleeping. One study found that groups of neurons in rats fire the same patterns while the rats negotiate a maze wide-awake and then while they slumber. In another study, also published in Science, people learned how to play the computer game Tetris. Later, when the subjects went to sleep, they were awakened throughout the night and asked to reveal their dreams. Nearly all reported they were dreaming about the computer game.
By replaying the day’s events in dreams, scientists argue, the brain is able to coalesce information it has taken in during the day and make sense of it.
“Practically all the experiments coming out to date say that your mother is right — that you need sleep before you train and learn and, most importantly, after you train and learn,” says Robert Stickgold, the Harvard psychologist who conducted the Tetris study.
Stickgold suspects that sleep deprivation may play a big role in learning problems and even in brain disorders — such as Alzheimer’s disease — that occur later in life.
Wiring Bird Brains
An important difference between sleep studies with humans and birds is how closely scientists are able to monitor the brain. Margoliash was able to track the activity of individual neurons while the zebra finches were both awake and sleeping. He did this by stringing a microwire inside the birds’ brains so they were near specific neurons. The wire then fed pulses reflecting the neurons’ activity to a recording device.
Scientists studying people’s brains during sleep can only dream of such intricate monitoring.
“You just can’t put a hole in someone’s head,” he says. “I have very dedicated graduate students but so far no one has volunteered.”
By tracking the activity of single neurons in the birds brains, the researchers saw that the cells fire in the same patterns when the bird is singing and when it is sleeping and listening to its own song. Those patterns are absent, however, when the bird is awake, not singing and is listening to a recording of its own song. So Margoliash concludes that sleeping is critical for the birds to rehearse their tune.
“In contrast to the prevailing idea that it learns by making moment-to-moment adjustments, we think the bird stores the song production pattern and reads it out at night,” Margoliash says. “The zebra finch can replay and strengthen the pattern during sleep.”