Fig. 2.
A reafferent and feed-forward model of song syntax generation (a) Combination of reafferent and feed-forward models. Each syllable (open circle) is connected in a feed-forward fashion (black arrows) to every syllable in the motor system, potentially allowing all syllable transitions. During syllable output the syllable is perceived by the auditory system (Aau), which responds by priming the activation of the next syllable in the motor system (blue arrows). The reafferent connections realize a specific song syntax; here, the perception of syllable ‘A’ results in excitatory input to syllables ‘A’ and ‘B’, thus sequences ‘AA’ and ‘AB’ will occur, but not ‘AC’ or ‘AD’. (b) Transition diagram for an example of Bengalese finch song syntax (Jin 2009). Each syllable is represented by a node, the black arrows connecting the nodes indicate possible transitions. (c) HVC interconnectivity. Each syllable is represented by a synfire chain. The final group of each chain makes feed-forward connections to the initial group of every chain, as shown for syllable ‘A’ in (a). (d) Auditory priming. Each synfire chain makes excitatory connections to the corresponding auditory sub-network. Each auditory sub-network makes excitatory connections to specific synfire chains to realize a song syntax. Color coding and syntax as in (b)