Inhibition protects acquired song segments during vocal learning in zebra finches
Fixation on learned syllables Zebra finches learn their beautiful songs by listening to other zebra finches. Vallentin et al. observed zebra finch brains as learning proceeded, only to find that inhibition of the neuronal circuits was critical to fixating on learned sequences. For song syllables that have been adequately learned, the inhibitory neurons fired coherently. Song syllables not yet learned failed to produce this flag. Thus, it is the learning process that alters the neuronal circuits. The inhibitory neuronal firing, not the age of the bird, locks in the learning. Science, this issue p. 267 Songs that birds have already learned are preserved by inhibitory neurons that block further modifications. Vocal imitation involves incorporating instructive auditory information into relevant motor circuits through processes that are poorly understood. In zebra finches, we found that exposure to a tutor's song drives spiking activity within premotor neurons in the juvenile, whereas inhibition suppresses such responses upon learning in adulthood. We measured inhibitory currents evoked by the tutor song throughout development while simultaneously quantifying each bird's learning trajectory. Surprisingly, we found that the maturation of synaptic inhibition onto premotor neurons is correlated with learning but not age. We used synthetic tutoring to demonstrate that inhibition is selective for specific song elements that have already been learned and not those still in refinement. Our results suggest that structured inhibition plays a crucial role during song acquisition, enabling a piece by piece mastery of complex tasks.
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