The study of how new neurons are made in the adult brain (adult neurogenesis) has received much attention because newborn neurons can integrate into and reshape preexisting neural circuits, making circuits “plastic.” It's not clear, though, how neural plasticity relates to the behavior produced by a particular neural circuit. Songbirds exhibit seasonal plasticity: during breeding season they have an increased number of neurons called Higher Vocal Center neurons (HVCs), which connect different regions of the brain important for producing songs. The relationship between cyclic addition/removal of HVC neurons and song production in male white-crowned sparrows was addressed by Rachel Cohen and colleagues. To compare the number of newly added HVC neurons to song quality in breeding versus non-breeding sparrows, they first had to count the number of newly added HVCs. They then compared this to the types of songs the sparrows sang. Cohen and colleagues found a direct correlation between song structure and HVC neuron number. When HVC neuron number goes down, song structure degrades (corresponding to non-breeding birds), but as new HVCs are added, song structure recovers (corresponding to breeding birds). Generation of new HVC neurons was also correlated to increases in the amount of a steroid hormone known to be important for neuron survival. The authors provide highly suggestive evidence that the underlying basis for circuit plasticity in this song circuit is the regeneration of HVC neurons, a process controlled by hormones. The seasonal plasticity of songbird neural circuits may also serve as a new model for understanding how number of neurons and the connections they make produces specific types of behaviors.
Jennifer Lovick (@drjkyl)
Senior Editor, Science in Entertainment, Signal to Noise Magazine
PhD, Molecular, Cell, and Developmental Biology