A team of researchers from Japan and South Korea has found that a set of neurons called corticobasal ganglia projecting neurons are important for vocal learning in juvenile birds, but not in adult birds.
A male zebra finch (Taeniopygia guttata) in Karratha, Pilbara, Western Australia. Image credit: Jim Bendon / CC BY-SA 2.0.
Birdsong, like human speech, is a series of precisely timed movements learned by copying the vocalizations of other individuals.
“The song system in birds shares a number of similarities with mammalian motor circuits,” said Dr. Kazuhiro Wada, a neuroscientist at Hokkaido University.
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, Dr. Wada and colleagues studied zebra finches (Taeniopygia guttata) and explored what happens when the neurons that connect the motor cortical area and the basal ganglia are disrupted.
The researchers injected a virus that expresses cytotoxic protein into the connecting neurons.
The toxins only killed these connecting neurons, which are called corticobasal ganglia projection neurons.
The authors 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.
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,” Dr. Wada said.
The findings were published in the Proceedings of the National Academy of Sciences.
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Miguel Sánchez-Valpuesta et al. 2019. Corticobasal ganglia projecting neurons are required for juvenile vocal learning but not for adult vocal plasticity in songbirds. PNAS 116 (45): 22833-22843; doi: 10.1073/pnas.1913575116
