Table 1.

Critical period markers in juvenile and adult song nuclei

Song nucleus	33 d olds and adults	Volume (mm³) (n birds)	%PV⁺ and PNN⁺ neurons	%PV⁺ neurons	%PNN⁺ neurons	%PV with PNN	%PNN with PV
HVC	33	0.053 ± 0.016^* ^* (7)	0.4 ± 0.2^** (6)	9.1 ± 5.3 (6)	0.6 ± 0.7^**	4.8 ± 6.3^** (6)	27.8 ± 44.3^* (6)
	Adult	0.188 ± 0.024^** (7)	3.3 ± 0.3^**	8.1 ± 2.4	3.8 ± 0.1^**	42.5 ± 11.7^**	86.4 ± 6.8^*
RA	33	0.058 ± 0.014^* (5)	1.3 ± 0.9^* (4)	19.4 ± 10.3 (4)	1.5 ± 1.8^*	11.6 ± 13.4 (4)	47.7 ± 55.2 (4)
	Adult	0.158 ± 0.027^* (7)	4.2 ± 0.7^*	18.9 ± 7.3	6.4 ± 3.2^*	23.0 ± 6.4	67.7 ± 10.6
Area X	33	0.291 ± 0.057^* (5)	0.7 ± 0.4 (4)	5.0 ± 0.8^** (4)	1.1 ± 0.9	13.7 ± 14.1^* (4)	58.2 ± 27.4 (4)
	Adult	0.876 ± 0.116^* (6)	0.9 ± 0.1	2.9 ± 0.4^**	1.8 ± 0.5	31.4 ± 9.4^*	50.7 ± 10.3
LMAN	33	0.0575 ± 0.022 (6)	1.2 ± 0.3^*	3.4 ± 1.5	1.8 ± 0.7	35.1 ± 22.6	63.3 ± 25.0
	Adult	0.0476 ± 0.007 (4)	2.4 ± 0.4^*	5.1 ± 2.4	2.8 ± 0.8	48.1 ± 11.3	83.2 ± 11.5

↵Data indicate mean ± SD. If not otherwise noted, the number of animals available for percentage calculations was the same as for volume. For given nucleus and measurement, adults and 33 d olds were significantly different (*p < 0.05, **p < 0.0005, unpaired two-tailed t test).