The boisterous songs a male zebra finch sings to his mate might not sound all that melodious to humans—some have compared them to squeaky dog toys—but the courtship tunes are stunningly complex, with thousands of variations. Now, a new study helps explain how the birds master such an impressive repertoire. As they learn from a tutor, usually their father, their brains tune out phrases they’ve already studied, allowing them to focus on unfamiliar sections bit by bit. The mechanism could help explain how other animals, including humans, learn complex skills, scientists say.
The study is a “technical tour de force,” and “an important advance in our understanding of mechanisms of vocal learning and of motor learning generally,” says Erich Jarvis, a neuroscientist at Duke University in Durham, North Carolina.
Many species—including humans, chimpanzees, crows, dolphins, and even octopuses—learn complex behaviors by imitating their peers and parents, but little is known about how that process works on a neuronal level. In the case of zebra finches, young males spend the whole of their teenage lives trying to copy their fathers, says Michael Long, a neuroscientist at New York University in New York City. It comes out “all wrong” at first, but after practicing hundreds of times, the birds “sound a lot like dad.”
In the new study, Long’s graduate student Daniela Vallentin used a tiny electrode implant to record the activity of neurons in a region of the finch brain called the HVC, which is essential for birdsong learning and production. Weighing less than a penny, the implant can be affixed to a bird’s head and record activity in the brains of freely moving and singing birds, Long says. The researchers also used a powerful light microscope to visualize the activity of individual neurons as the birds listened to a fake “tutor” bird that taught young finches only one “syllable” of a song at a time.
By eavesdropping on neural activity as the birds learned new songs, the team noticed that one group of neurons in this region, called premotor neurons, fires whenever a juvenile or adult bird hears its tutor’s song. Premotor neurons typically activate before the onset of anticipated movements. “It’s kind of amazing,” Long says. “Just listening to dad is enough to make the premotor cells fire.”
A second group of neurons, called inhibitory interneurons, connects to the premotor neurons and dampens their activity. As the birds grew more accurate in their imitation of a tutor’s songs, inhibitory neurons fired more frequently and in a more regular pattern, suppressing the response of premotor neurons whenever the young birds heard phrases they had mastered, the group reports online today in Science. “We see that the brain changes how it listens to the father once it’s learned part of that song,” essentially becoming more independent as it learns, Long says. “It’s kind of a sweet story.”
Long believes the inhibitory cells help suppress a tutor’s input once it’s no longer needed, locking in what the bird has already learned while also allowing it to move on with unfamiliar parts of the song. Inhibition was strongly correlated with accuracy, not age, suggesting that song-learning is different from skills that are highly age-dependent, like vision, he adds.
But Jarvis sees more similarity than difference between the acquisition of these two skill sets. Both song-learning and vision require inhibitory input, which kicks in with exposure to external stimuli (like the tutor’s song). Still, he says, “one could easily see” the findings translating to humans in a range of activities, from language acquisition to dance.