Fig. 8.

Model of the vocal central pattern generators (CPGs) in male X. laevis. A: functional model of the central vocal pathways of male X. laevis. Green ovals and blue circles containing sinusoidal waveform indicate CPGs for fast and slow trills, respectively. B: four different types of anatomically identified projection neurons in the central vocal pathways of X. laevis. Axons of these neurons are contained in anterior or posterior commissures. C: blue arrows indicate hypothesized redundant mechanisms of vocal initiation by serotonin (5-HT).