Development of perineuronal nets during ontogeny correlates with sensorimotor vocal learning in canaries

Songbirds are a powerful model to study vocal learning given that aspects of the underlying behavioral and neurobiological mechanisms are analogous in many ways to mechanisms involved in speech learning. Perineuronal nets (PNNs) represent one of the mechanisms controlling the closing of sensitive periods for vocal learning in the songbird brain. In zebra finches, PNN develop around parvalbumin (PV)-expressing interneurons in selected song control nuclei during ontogeny and their development is delayed if juveniles are deprived of a tutor. However, song learning in zebra finches takes place during a relatively short period of development, and it is difficult to determine whether PNN development correlates with the end of the sensory or the sensorimotor learning period. Canaries have a longer period of sensorimotor vocal learning, spanning over their first year of life so that it should be easier to test whether PNN development correlates with the end of sensory or sensorimotor vocal learning. Here, we quantified PNN around PV-interneurons in the brain of male canaries from hatching until the first breeding season and analyzed in parallel the development of their song. PNN development around PV-interneurons specifically took place and their number reached its maximum around the end of the sensorimotor learning stage, well after the end of sensory vocal learning, and correlated with song development. This suggests that PNN are specifically involved in the termination of the sensitive period for sensorimotor vocal learning.