(a) PVALB and C-FOS mRNA expression in the NLC and AAC core and shells. (i) PVALB specialized mRNA expression in the NLC and AAC core and shell, as well as adjacent motor areas; (ii) Vocalizing-driven C-FOS mRNA expression in the NLC and AAC core and shells; (iii) Movement-induced C-FOS mRNA expression in parts of the shell regions around NLC and AAC; (iv) Lack of hearing-induced C-FOS mRNA expression in the NLC and AAC song nuclei in a silent bird. (b) PVALB and C-FOS mRNA expression in the MO and NAO of the anterior vocal pathway in birds. (i) PVALB mRNA expression in the MO core; (ii) PVALB mRNA expression in the NAO core; (iii) Vocalizing-induced C-FOS mRNA expression in the MO and NAO core and shells, and the MMSt song nucleus; (iv) Movement-induced C-FOS mRNA expression in the areas surrounding the MO and NAO core and shells, and the MMSt song nucleus. Sections are in the coronal plane; medial is to the left, dorsal is top. Some sections are from the same animals used in experiments of Feenders et al. [35] (a-iii, b-iv), Jarvis and Mello [24], and Jarvis [44] (a-ii, a-iv, b-iii, b-iv). See list for Abbreviations.