Experience Affects Recruitment of New Neurons But Not Adult
Neuron Number
Linda Wilbrecht, Alex Crionas, and Fernando Nottebohm
Laboratory of Animal Behavior, The Rockefeller University, New York, New York 10021
It is not known whether the addition of new neurons to the high
vocal center (HVC) of juvenile zebra finches permits vocal
learning or is the consequence of it. To tease apart these two,
we performed surgery on 26-d-old juveniles. The operations
were removal of both cochleae and unilateral or bilateral dener-
vation of the syrinx. Ability to imitate a tutor song was little
affected by unilateral syringeal denervation but was severely
hindered by bilateral denervation or deafening. Recruitment of
new HVC neurons was studied by injecting BrdU, a cell birth
marker, on post-hatching days 61–65 and killing the animals
30 d later. Deafening or bilateral denervation did not alter the
number of BrdU-labeled neurons in HVC, but unilateral dener-
vation nearly doubled this number in the intact side. This dou-
bling was transient, was blocked by deafening, and was not
seen in birds that received BrdU injections earlier or later in
vocal ontogeny. The adult number of HVC neurons was not
affected by any of our surgical procedures. Apparently experi-
ence does not affect the total number of neurons in adult HVC,
but some kinds of experience can, during narrowly defined
times, influence the recruitment of new HVC neurons.
Key words: song learning; neurogenesis; BrdU; unilateral
denervation; sensitive period; syrinx
Many new neurons are added to the song system of birds during
periods of song acquisition, both in juveniles (Alvarez-Buylla et
al., 1988, 1990; Nordeen and Nordeen, 1988; Nordeen et al., 1989)
and in adults (Kirn et al., 1994), suggesting that new neurons
might underlie the exceptional behavioral changes that take place
then. Changes in new neuron numbers in the hippocampus of
birds (Barnea and Nottebohm, 1994) and mammals (Kemper-
mann et al., 1997; Gould et al., 1999; Shors et al., 2001) have also
been sho