In songbirds, "FOXP2" most likely regulates genes involved in neuroplasticity. Gene knockdown of "FOXP2" in area X of the basal ganglia in songbirds results in incomplete and inaccurate song imitation. Overexpression of FoxP2 was accomplished through injection of adeno-associated virus serotype 1 (AAV1) into area X of the brain. This overexpression produced similar effects to that of knockdown; juvenile zebra finch birds were unable to accurately imitate their tutors. Similarly, in adult canaries, higher "FOXP2" levels also correlate with song changes.