16 March 2018
Stephanie White
Department of Integrative Biology and Physiology
UCLA
Long before they learn to sing, baby songbirds, like human babies, cry for attention. Only through long hours of practice during a 'critical period' do they develop a song suitable for courting mates. Human language also blossoms during a critical period whose closure makes it difficult to speak a foreign tongue. Remarkably, the act of singing reduces levels of the language-related transcription factor, FoxP2, within song control cells of the avian striatum, along with coordinated changes in thousands of other genes. These changes occur in young and old birds. Changes unique to young birds may underlie critical period learning.
Birds and humans share a long and short version of FoxP2. Humans with a mutant long version have abnormal speech and abnormal striata. When the long version is experimentally perturbed in bird striatum, song learning is impaired. The short version has no known behavioral role. We set out to identify how the coordinated expression of genes in song control cells shifts across the critical period boundary. In particular, we sought patterns correlated to learning as these could comprise the molecular basis of critical period plasticity. We were also curious about the behavioral effects of altering short FoxP2, common to human brains.
We found sets of genes in young birds whose levels change in concert and are tightly linked to levels of learning. These patterns were lost in old birds. Several of these genes are essential to human language development. We replicated our discovery that perturbing long FoxP2 disrupts learning. We were surprised that perturbing the short version did not. Rather, it led to less variable song, raising questions about the role of variability in motor learning.