Song-learning neurons identified in songbirds

A group of neurons called the corticobasal ganglia projecting neurons are important for vocal learning in young birds, but not in adult birds, according to a study published in the journal Proceedings of the National Academy of Sciences (PNAS).


The zebra finch used in the study.

Birdsong, like human speech, is a series of precisely timed movements learned by copying the vocalizations of other individuals, such as parents.

“The song system in birds shares a number of similarities with mammalian motor circuits,” says Kazuhiro Wada, the Hokkaido University neuroscientist who led the study.

In birds, the song learning process depends on specific brain regions called the motor cortical area and the basal ganglia – these regions are also found in the mammalian motor system and are important for learning and maintaining sequential movements. However, it is unknown what role the neural connections between these two regions play.

To investigate this, the researchers studied zebra finches, a type of songbird, and explored what happens when the neurons that connect the motor cortical area and the basal ganglia are disrupted. They injected a virus which expresses cytotoxic protein into the connecting neurons. The toxins only killed these connecting neurons, which are called corticobasal ganglia projection neurons.


The neurons connecting the motor cortical area and the basal ganglia in the brain were disrupted using viral toxins (left: normal, right: disrupted). This interrupted normal song learning in juveniles but not adults. (Miguel Sánchez-Valpuesta et al., PNAS, October 21, 2019)

They found that juvenile zebra finches with disrupted projection neurons could not copy song patterns and developed unusual songs with inconsistent sequences. When they repeated the same experiments in adult birds, they found that birds with disrupted projection neurons did not alter their pre-learned song structure and showed normal vocal fluctuations.

https://www.global.hokudai.ac.jp/wp-content/uploads/2019/10/Fig3a-Control-birds-at-ad.mp3https://www.global.hokudai.ac.jp/wp-content/uploads/2019/10/Fig3b-HVCx-lesioned-juv-at-ad.mp3

Birdsongs sung by a normal zebra finch (top) and a zebra finch with disrupted projection neurons (bottom).

The results imply that the corticobasal ganglia projection neurons are important for learning the acoustic and temporal aspects of a song’s structure, but not for maintaining an already learned vocal pattern.

“Studying the corticobasal ganglia circuit may enhance our understanding of vocal development and communication disorders in humans,” says Kazuhiro Wada.

This study was conducted with colleagues at The University of Tokyo, the National Institute for Physiological Sciences, Tokyo Metropolitan Institute of Medical Science in Japan, and the Korea Brain Research Institute.


Associate Professor Kazuhiro Wada (left) and Miguel Sánchez-Valpuesta (right) of the research team at Hokkaido University.

Original article:

Miguel Sánchez-Valpuesta et al., Corticobasal ganglia projecting neurons are required for juvenile vocal learning but not for adult vocal plasticity in songbirds. Proceedings of the National Academy of Sciences of the United States of America (PNAS), October 21, 2019.

Funding:

This study was supported by MEXT/JSPS KAKENHI (JP17H01015, #4903-JP17H06380, JP19H04888, JP17K19629, and JP18H02520).

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