A new study by neuroscientists at Emory University suggests that oxytocin, known as the “love hormone,” plays a key role in the process of young zebra finch learning to sing by imitating its elders. Scientific reports publish the results, which add to the understanding of the neurochemistry of social learning.
“We found that the oxytocin system is involved from an early age in male zebra learning song,” says Natalie Pilgrim, first author of the study and PhD candidate in psychology. “It is basic science that may lead to insights into the vocal learning process across the animal kingdom, including humans.”
“Our findings suggest that the neurochemistry of early social bonds, particularly during language learning, may be relevant to studies of autism,” adds Donna Mane, associate professor of neuroscience in the Department of Psychology at Emory and lead author of the study.
Male zebra finches learn to sing by listening to an adult male tutor whom they choose to pay close attention to, usually their biological father or “foster” father who is caring for them. This social process bears some similarities to how babies learn to speak, making birds a laboratory model for the neural underpinnings of social vocal learning.
In the current paper, the researchers show how oxytocin, a hormone essential for social bonding, affects young finches exposed only to the songs of unfamiliar males. In experiments, blocking young birds’ oxytocin receptors while listening to a male biased the birds against that male’s song. Instead, they preferred to listen to a male song that they eventually heard and learned when their oxytocin receptors were allowed to function normally.
The paper builds on previous work by Mani’s lab regarding hormonal and genetic influences on social behavior. Her lab works with researchers at the Marcus Autism Center in Atlanta to maximize any potential translational impact of its research findings.
Zebra finches are very social birds. In the wild they nest together in large colonies. Only adult males sing, primarily to court females.
From the time they hatch, males begin song listening and memorizing certain songs, even before they can actually sing one. “Until about day 50, they would make little purrs and songs, which we call ‘sub songs,’” Pilgrim explains. “It’s similar to babies starting to babble at around six months without actually speaking.”
During this sensitive listening phase, the male zebra finch pays close attention to his father’s song, even though he can hear other adult males nearby.
In a laboratory setting, research shows that if a biological father is removed from a cage before a male hatches and then replaced with a “foster father” with whom they can interact, the young will prefer the song of the adoptive father over other males that can be heard. Young males display this preference by pressing levers that allow them to hear the playing of various songs.
“Young birds should learn as much as they can from their environment,” says Pilgrim. “Just as during human development, birds pay close attention to their immediate caregivers, on whom they depend for everything.”
Around the 50th day, male finches enter adulthood and what is called the “plastic song stage”. During this time, they practice their motor skills in songs and actively try to produce songs. Although they begin to turn their attention away from their fathers and show a preference for hearing the songs of other males, each young man still plays the father’s tune.
By day 100, most male zebra finches have completely sung their father’s song. They’ve come of age and “crystallized” their tune into the song they’ll sing for the rest of their lives.
In previous research, Manny’s lab found that the stronger a male zebra finch’s preference for his father’s song during the early listening phase, the more his adult song mimicked the father’s song.
For the current paper, the researchers wanted to test whether the oxytocin system played a role in this preference.
The research focused on young male zebra finch hatched in the laboratory. On the fourth day, the fathers were removed from the cages of each of the young so that they would be raised solely by their mothers. The cages were surrounded by chambers that prevented the young birds from hearing a song from other birds in the vicinity.
Beginning on the 27th day of the young bird’s life, he was subjected to a series of tutoring sessions by two adult male teachers who had never heard of him. The teacher’s cage was placed next to the cage of the young bird or pupil. When exposed to a teacher, the pupil was given a substance that blocks oxytocin receptors from being activated. When the baby bird was exposed to the other teacher, it received a control substance that allowed its oxytocin receptors to function normally.
After completing a series of private lessons, the pupils were presented with two different levers that they could press into their cages. Pressing one lever was more likely to play the song they heard when their oxytocin receptors were blocked. The other lever was more likely to play the song they heard with naturally occurring oxytocin.
The results showed that early in their development, juveniles preferred the song they heard when their oxytocin was not blocked.
“We also found that when their oxytocin was not inhibited, the birds’ developmental milestones fit along the same data curve as in our previous research,” says Mani. “They showed an early preference for one teacher’s song, and then switched to a preference for the other song during puberty.”
She adds that preference prevailed when they began to sing their chosen teacher’s song. The greater the preference they showed for the chosen teacher’s song during the early listening phase, the more similar their adult song was to the chosen teacher’s song.
The researchers also noted behavioral differences in the way pupils and teachers interacted. With naturally functioning oxytocin, the pupil tapped more often on the wall of the cage facing the teacher and was more often primed in a manner known to be associated with focused listening in birds, compared to when oxytocin was withheld.
“Our results suggest that the oxytocin system is involved in the way an animal decides where to focus its attention very early in its life,” says Pilgrim.
One of the study’s co-authors is Carlos Rodriguez-Saltos, who received his Ph.D. from Emory and is now at Illinois State University. Postdoctoral Fellow Nicole Baran. research technologists Matthew Davis and Eric Iverson; and Emory alumni Soomin Lee, Emily Kim, and Aditya Beezy.
The work was funded by the National Institutes of Health and the Silvio O. Conte Center for Oxytocin and Social Cognition.