Postlearning consolidation of birdsong: Stabilizing effects of age and anterior forebrain lesions

Birdsong is a learned. sequenced motor skill. For the zebra finch, learned song normally remains unchanging beyond early adulthood. However, stable ad ult song will gradually deteriorate after deafening (Nordeen and Nordeen, 1 992), indicating an ongoing influence of auditory feedback on learned song. This plasticity of adult song in response to deafening gradually declines with age (Lombardino and Nottebohm, 2000), suggesting that, after song lear ning, there continue to be changes in the brain that progressively stabiliz e the song motor program. A qualitatively similar stabilization of learned song can be precipitated artificially by lesions of a basal ganglia circuit in the songbird anterior forebrain (Brainard and Doupe, 2000), raising the question of whether and how these two forms of song stabilization are rela ted. We investigated this issue by characterizing the deterioration of song that occurs after deafening in young adult birds and the degree to which t hat deterioration is reduced by age or by lesions of the anterior forebrain that were directed at the lateral portion of the magnocellular nucleus of the anterior neostriatum (LMAN). In most respects, LMAN lesions stabilized song to a significantly greater extent than did aging; whereas old-deafened birds eventually exhibited significant deterioration of song, lesioned-dea fened birds generally did not differ from controls. The one exception was f or song tempo, which was significantly stabilized by age, but not by LMAN l esions. The results indicate that LMAN lesions do not simply mimic a normal aging process, and likewise suggest that the anterior forebrain pathway co ntinues to play a role even in the residual song plasticity that is observe d after the age-dependent stabilization of song.