Figure 1. Remodeling of the axonal projection from a cortico-basal ganglia circuit to vocal motor cortex in zebra finches.

The core region of LMAN (lateral magnocellular nucleus of the anterior nidopallium) provides the cortical outflow of a basal ganglia circuit necessary for vocal learning to vocal motor cortex (RA, robust nucleus of the arcopallium). Previous work from our lab has shown that the axons of LMAN_core form a precise topographic map in RA of adult birds (shown schematically in the upper right panel), which may represent a myotopic map of vocal muscles and/or acoustic features or vocal sounds. However, the axonal projection from LMAN_core to RA has little or no topographic organization in 20-day birds at the onset of vocal learning (20 d, upper left panel): axons from small subregions of LMAN_core spread throughout most of RA at this age [24], [69]. However, LMAN_core axons of birds that receive normal auditory experience undergo substantial re-modeling to form a normal topographic map by 35 days of age (35 d, lower left panel) [24]. In contrast, this axonal remodeling is prevented in juvenile birds that are raised in constant white noise [24]. This remodeling is due to both pruning and re-positioning of individual axons, including both genetic and experience-dependent changes in neural connectivity during the first two weeks of vocal learning [25]. Scale bars = 200 um.