How do songbirds learn their melodies? Scientists reveal clues.
Human babies seem to have a natural knack for languages. Fluency in any of the world鈥檚 6,500 languages comes within the first few years of life, without much apparent effort.
A recent study of how songbirds learn their melodies seeks to shine light on the cognitive processes through which young birds learn and imitate vocal communication 鈥撀爄nsights which could lead to a better understanding of the development of human speech, as well.
鈥淎 bird鈥檚 baby song is really immature. There鈥檚 no clear structure - it鈥檚 more like a baby babbling, but then it becomes structured, like the tutor song [as the bird gets older],鈥� Yoko Yazaki-Sugiyama, co-author of the study , tells 海角大神 in a phone interview.
The male zebra finch learns a complex song from his father, or tutor, in order to attract a female finch. Dr. Yazaki-Sugiyama, an assistant professor at the Okinawa Institute of Science and Technology Graduate University in Japan, and Shin Yanagihara, a researcher at the same school,聽were the first to identify the neurons in zebra finches鈥� brains associated with the auditory memory of the father鈥檚 song.
The pair聽studied young zebra finches in the critical period of development, when brain circuits are considered very flexible, to examine the impact of auditory experiences, particularly listening to a tutor's song.
Zebra finches begin memorizing their tutor's song between 20 and 50 days after hatching. At first, they just listen and make crude vocalizations, but by 90 days old , based off their tutor鈥檚 song, according to a previous study from scientists at the University of Illinois, Urbana.聽
The evolution from silence to babbling to a distinctive melody is apparently made possible by the experience of listening to the bird's father鈥檚 song to form a memory. Once the birds have the tutor's song memorized, they try to mimic it.
The researchers monitored the neuronal auditory response of both tutored and isolated birds listening to their own song, their tutor鈥檚 song, other zebra finches鈥� songs, and different songbirds鈥� songs. The study revealed that about 5 percent of the tutored bird鈥檚 neurons, or 27 neurons, responded exclusively to their tutor鈥檚 songs.
"In the normal, tutored birds, we encountered a group of neurons that responded very strongly to the tutor song, after they had learned the song, but did not respond to the other songs," Dr. Yanagihara . "However, for the birds which had no tutor experiences, we did not see any response to the tutor-song, or in this case the genetic-father-song, and no selective neurons at all."
Scientists predict that the selective neurons that respond to the tutor鈥檚 song represent the part of the higher auditory cortex where early auditory memory is located in the brain.
"We believe that these tutor song selective neurons represent the memory of the tutor song and that learning the tutor song during the critical period changes the neural circuits to accommodate this memory,"聽Yanagihara said.
Another finding was that the neurons of sleeping birds were less selective than those of awake birds, meaning they responded to other songs in addition to the tutor song.
As for the implications for human language, Yazaki-Sugiyama聽tells the Monitor that researchers believe that the human brain is also "wired" based on early sensory experiences. But the zebra finch song is much simpler than human speech: it鈥檚 a behavior to attract females, rather than a way to convey information. Additionally, each zebra finch has only one distinctive melody.
鈥淥nce they develop their own song, it doesn鈥檛 change. Each individual has their own specific song that makes them individual. They learn only one thing,鈥� says Yazaki-Sugiyama.
