AsianScientist (Jun. 23, 2016) – Researchers in Japan have identified the neurons in the brain that are associated with song-learning in young zebra finches. Their findings, which could provide insights into human speech development, have been published in Nature Communications.
Learning a first language is somewhat effortless; the words and sounds are imprinted in our memory at an early age. Learning a new language as an adult is much more difficult. The same is true of songbirds—zebra finches learn to sing when they are young by listening to their father’s or tutor’s song.
“For young animals, the early sensory experiences are very important and strongly affect brain development. This stage is called the ‘critical period’ where the brain circuits are very flexible and can be easily changed and modified,” said Dr. Shin Yanagihara, staff scientist in Okinawa Institute of Science and Technology Graduate University’s Neuronal Mechanism for Critical Period Unit.
In zebra finches, only males learn and sing songs, as this is the way they attract a mate. Juvenile zebra finches do this by listening to their father’s song and memorizing it. When they begin to vocalize, it is thought that through their auditory memory of the tutor song, they can recall the sounds until they develop their own.
“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 their father’s song, these experiences modify the juvenile birds’ brain circuits to form a memory of it.”
The researchers looked at the response of neurons in the higher auditory cortex, which is a part of the specialized neural circuit, 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 control birds.
Information collected from single neurons showed that there were non-selective neurons that responded to all the songs, but also selective neurons that had a very selective, and in many cases, exclusive, response to the tutor songs. Approximately five percent of the neurons in the higher auditory cortex reacted to the tutor song; this could be indicative of where the early auditory memory is located in the brain.
“We found 27 neurons that selectively respond to the tutor song,” Yanagihara said. “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.”
The article can be found at: Yanagihara & Yazaki-Sugiyama (2016) Auditory Experience-Dependent Cortical Circuit Shaping for Memory Formation in Bird Song Learning.
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Source: Okinawa Institute of Science and Technology Graduate University.
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