Research scientists at Okinawa Institute of Science and Technology Graduate University (OIST) in Japan have found that human language learning and songbird language learning have similarities.
For humans, learning a first language can be considered somewhat effortless. We start learning from our parents before we can even remember, and the words and sounds are imprinted in our memory at an early age. Learning a new language as an adult is much more difficult, involving hard work, and we may never gain the same fluency that we have with our first language.
Recently, Yazaki-Sugiyama and Yanagihara identified, for the first time, the neurons in the brain that are associated with the auditory memory of the father’s song in zebra finches, which could lead to deeper insight into human speech development. Their findings are outlined in an article published in the June 21, 2016 edition of Nature Communications.
“For young animals, the early sensory experiences are very important and strongly affect brain development,” said Yanagihara, staff scientist in OIST’s Neuronal Mechanism for Critical Period Unit. “This stage is called the ‘critical period’ where the brain circuits are very flexible and can be easily changed and modified.”
Yanagihara and Yasaki-Sugiyama wanted to know how the early sensory experiences during the critical period shape brain circuits and lead to appropriate behaviors. In zebra finches, only males learn and sing songs, as this is the way they attract a mate. Therefore, learning a complex song to attract the female zebra finches is crucial for reproduction. The juvenile zebra finches do this by listening to the father’s song and memorizing it. When they begin to vocalize, it is thought that through their auditory memory of the tutorial song, they can recall the sounds and gradually adapt the song until they develop their own song, which is comparable to their tutor’s song.
“This is similar to human speech development,” Yanagihara said. “During the critical period children listen to adult speech and their brain circuits are shaped to capture auditory features of that speech. We predicted that when birds listen to the father’s song, these experiences modify the juvenile birds’ brain circuits to form a memory of it.”
To confirm their hypothesis and learn more about where the memory of the tutor song is stored, the researchers reportedly looked at the response of neurons in the higher auditory cortex to the sound of the tutor song. They monitored the neuronal auditory response when the birds listened to different songs – their own, the tutor, other zebra finches, and the songs of different songbird species – in tutored juvenile birds and in isolated juvenile birds (the control group).
The researchers monitored responses in single neurons and collected the information from many neurons in the birds and found that there were non-selective neurons that responded to all the songs, but also selective neurons that had a very selective response to the tutor songs.
“In the normal, tutored birds, we encountered a group of neurons that responded very strongly to the tutor song, but did not respond to the other songs,” Yanagihara said. “However, for the birds that had no tutor experiences, we did not see any response to the tutor-song, or the genetic-father-song, and no selective neurons at all.”
The team found that approximately 5% of the neurons in the higher auditory cortex reacted to the tutor song and that this could be indicative of where the early auditory memory is located in the brain. The researchers 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.”
This is an important finding because the brain mechanisms during the critical period are still not very well understood. These findings could be a step in grasping how the brain circuit is shaped during early stage development and how these neuronal circuits contribute to higher cognitive function in adulthood, not only in birds, but also in humans and other species.
Source: Okinawa Institute of Science and Technology Graduate University (OIST); Nature Communications