Figure 4 |. Hypothesized model for aligning behavioral-goal memories and descending motor commands for song evaluation.

In this model, the behavioral-goal memory of the tutor song is represented in motor coordinates within HVC and is used to guide vocal learning. The known HVC neuronal subpopulations are represented (black, interneurons; blue, HVC_X; red, HVC_RA; green, HVC_Av). Connections to the end target nuclei and/or to HVC neuronal subpopulations are indicated by bifurcated axonal aspiny terminations onto the brain nuclei (or on the dendritic trees of the target neurons) (Mooney and Prather, 2005; Roberts et al., 2017). In this model, each HVC_RA neurons conveys to RA information about a specific moment in song (t_0-n). A copy of this signal is used locally in HVC, via local axonal collaterals of HVC_RA neurons, to recall the behavioral-goal memory for each moment in the song. Signaling through HVC_Av neurons, a temporally registered predictive signal that represents the behavioral-goal memory for each time-step in the song is relayed to Avalanche. Once in the auditory system, this behavioral-goal memory is compared with the auditory feedback to evaluate song performance.