Fig. 5.

Recurrent network model. HVC is divided into syllable and gap chains which are further divided by their medial or lateral locality. Syllable chains directly control the activity of the expiratory nucleus RAm, and neurons in the lateral syllable chains initiate PAm activity and gap chains. HVC gap chains control the duration of inspiratory activity; however, activity within PAm is controlled outside HVC. Neurons in the medial HVC chains initiate the next syllable. Initiation of a syllable leads to the termination of the inspiratory PAm activity and the initiation of expiratory activity. Mutually inhibitory, song unit-specific Uva neurons initiate song units and ensure that only one song unit activates at a time.