The Connections of NIf-HVC and Vocal Learning and Maintenance in the Songbirds

Birdsong and human languages are both acquired by learning. During sensory period, templates are formed in the brain after juveniles hear tutor songs and stored in the related areas and in the motor-learning phase, juveniles compare their own songs to the templates and modify them to match the templates in their memories. When the songs are crystallized in the adult stage, auditory feedback is required to maintain the features and stability of their own songs. Hence, the sensory-motor integration of auditory and motor systems is vitally important to the formation of templates and the maintenance of crystallized songs. In the recent years, it is found that NIf-HVC synapses are related with the formation of templates memory and the maintenance of spatial features of plastic songs in the juveniles while this projection is crucial for the grammar structure of crystallized songs in the adults. NMDAR、AchR and NE may be involved in modulating the strength of synapses of NIF-HVC. In songbirds, HVC shares resemblance with human Broca's Area and NIf has many similarities with Area Spt in the human speech processing circuit. Therefore, the research about the function of NIf-HVC synapses in the speech circuit is not only helpful for the study of Area Broca and Spt of human but advantageous for exploring the mechanism concerning sense and motion information integration involved in vocal learning.