If we’re lucky, we spend about one-third of our lives sleeping, a fact that appears on its face to be a colossal waste of time. Wouldn’t us humans be able to get so much more done if we weren’t required to shut down for 8 hours a night? But the fact that the need for sleep is shared across the majority of animal species indicates that there must be some important role that the behavior plays, otherwise evolution would have likely done away with it millions of years ago.
The laboratories of Daniel Margoliash and Howard Nusbaum at the University of Chicago focus on how birds and humans learn to use language. But over the past decade, their research has also discovered some pretty interesting things about the role that sleep plays in language learning. In Margoliash’s laboratory, studies of juvenile zebra finches learning to sing found that the brains of birds will “replay” in sleep the symphony of neural activity that was present during the day when they listened to song. Separate human studies by Margoliash and Nusbaum found that sleep helped stabilize the learning of a language perception task - college students learning to comprehend computer-generated speech similar to heavily-accented English performed better on the task after a night’s sleep.
The latter experiment tested the principle of memory consolidation, the process by which short-term memories are stabilized into long-term storage. Sleep’s role in facilitating consolidation has been studied in many different ways in humans, including a 2008 paper by Timothy Brawn and Kimberly Fenn with Margoliash and Nusbaum that found that sleep enhanced people’s ability to learn how to play a first-person shooter video game. But despite accumulating evidence in humans that sleep-dependent consolidation was a real phenomenon, a true animal model had not yet been established. So Brawn once again used the unique partnership between Margoliash and Nusbaum to demonstrate that the stabilization of memories through sleep was not a uniquely human characteristic, but was also present in a bird species, the starling.
In the video below, you can hear Brawn, Margoliash and Nusbaum talk about the experiment, which was published today in The Journal of Neuroscience. You can also watch one of the experimental subjects – a starling – perform the learning task that was used in the experiment, called a “go-nogo” task. After a day of learning what birdsong cue signaled them to poke their beaks into a hole to receive food, and what cue meant to avoid poking, the starlings were tested before and after a period of sleep. As in humans, sleep improved the starlings’ performance of the task, suggesting that sleep-dependent consolidation is a common feature of at least two species.
“We really wanted to behaviorally show that these types of sleep-dependent memory benefits are occurring in animals,” Brawn said. “What was remarkable was that the pattern here looks very similar to what we see in humans. There wasn’t anything that was terribly different.”
Now that the similarities between birds and humans have been proven for this phenomenon, the story is just beginning. Further experiments in the starlings will look for the mechanisms of how sleep-dependent consolidation occurs, offering clues to how memories are stabilized in the brain that would be difficult or impossible to gather from human studies alone.
“The result suggests this is a very broad, general phenomenon that might be shared across a great many vertebrates,” Margoliash said. “It was quite important to show that and it now opens the possibility for mechanistic and behavioral experiments in animals that are difficult to do in humans.”