By observing the effects of targeted manipulations on singing, we can infer the role and function of given brain regions and neural mechanisms. Ways in which we perturb the song circuit include pharmacology, electrical stimulation, and lesions.
A recent example of this approach is the inactivation of LMAN, the output nucleus of a basal ganglia circuit that projects to motor area RA. By infusing a blocker of neural activity into LMAN in the juvenile bird, the otherwise variable song became stereotyped. Thus, a simple perturbation made it possible to infer the function (induction of song variability) of a given brain region (LMAN) relative to the process of song learning.
We are now in the process of expanding our toolbox to include molecular techniques for manipulating brain circuits.
Inactivation of LMAN significantly reduces vocal experimentation, making the otherwise variable song of the juvenile zebra finch highly stereotyped.
(Top) To inactivate the output of the AFP, injections of TTX and muscimol (red bolus)were made into LMAN.
(Middle) Examples of a juvenile zebra finch song (57 dph) showing large variability in sequence and the acoustic structure of song syllables.
(Bottom) Inactivating LMAN with TTX produces an immediate reduction of sequence and acoustic variability, revealing a highly stereotyped song produced by the motor pathway.