Nottebohm (1965), in His Study of the Neurology of Birdsong

Nottebohm (1965) , in his study of the neurology of birdsong, made use of the fact that new neurons will incorporate chemical markers when they make DNA in preparation for cell division, but that old neurons do not, because they do not synthesize DNA. This information allowed him to demonstrate that

A) the increase in RA volume was due to changes in neuron size, but that changes in the HVC was due to appearance of new neurons.
B) the two song centers, the HVC and the RA, were interconnected, but only during initial song learning.
C) the volume of two song centers in the brains of male zebra finches, the HVC and the RA, increase and decrease seasonally.
D) there is actually little relationship between the addition of new neurons and song learning in male zebra finches.