Fig. 3: Reversal of FoxP2 knockdown in adult zebra finches rescues vocal repetitions but not disruptions in song syntax.

a Strategy for FoxP2 rescue in Area X. b Comparison of the number of syllable repetitions per song bout (mean ± SEM) at baseline versus 2 months after injection of CS-shFoxP2 or Cre-GFP (n = 5 birds). Red filled circles represent vocal elements with significant differences between baseline and post CS-shFoxP2 injection (p < 0.0001 and p = 0.012, Kruskal–Wallis test); green open circles, vocal elements with nonsignificant differences (p > 0.2, Kruskal–Wallis test); green filled circles, vocal elements with significant differences (p = 0.014 and p = 0.027, Kruskal–Wallis test) between baseline and post Cre-GFP injection. The number of syllable repetitions after Cre-GFP injection was significantly lower than the number of repetitions of the same syllables after CS-shFoxP2 injection (p = 0.016, n = 7, Wilcoxon signed-rank test). c Changes in the number of repeats per song bout, expressed in units of d’, for CS-shFoxP2+ birds (n = 5 birds) 2 months following CS-shFxoP2 injection (d′ = 1.94 ± 0.21[mean ± SEM]) and 3 months following Cre-GFP injection (d′ = −0.011 ± 0.27[mean ± SEM]). Changes in the number of repetitions relative to baseline were significantly decreased following Cre-GFP injection (p = 0.016, Wilcoxon signed-rank test). d % syntax alterations for CS-shFoxP2+ birds (n = 5 birds) 2 months following CS-shFxoP2 injection and 3 months following Cre-GFP injection. Changes were significantly greater than zero following Cre-GFP injection (p = 0.033) but not following CS-shFoxP2 injection (p = 0.084, one tailed one sample t-test). The frequencies of syntax alterations were not significantly changed following Cre-GFP injection (p > 0.99, Wilcoxon signed-rank test). e Left panel: spectrograms of song from one bird at baseline, 4 months after CS-shFoxP2 injection, and 3 months after Cre-GFP injection. The number of repetitions of introductory elements ‘i’ and syllable ‘d”(red) gradually increased and novel vocal elements (syllables ‘e’, ‘g’, ‘g”) emerged. Each letter indicates an individual syllable. Syllables ‘b”, ‘d” and ‘g” are variants of syllables ‘b’, ‘d’, and ‘g’, respectively. Scale bar, 200 ms. Right panel: difference transition matrices. Subtracting the syllable transition matrix at 4 months following CS-shFoxP2 injection (top) or at 3 months following Cre-GFP injection (bottom) from the matrix at baseline reveals changes in the syllable transitions during reversible knockdown of FoxP2.