Figure 7.

Modulating the structure of motor variability through specific muscle synergies. A, A schematic illustrating how increasing the variability of a specific W or its C from session 1 (green circle) to session 3 (blue ellipse) could result in score gain. Score gain can be facilitated if W or C variability is modulated such that the subspace of motor commands from W and C is enlarged towards the command subspace that is conducive to scoring. B, A hypothetical neural circuit for modulating learning-relevant motor variability. The conjectured human homolog of the finches’ LMAN injects variability to the higher motor areas for generating the C for a specific synergy (solid purple line), and for young adults only, to the lower-level brainstem/spinal circuits for structuring that synergy, W (dotted purple line). Reward signals from successful actions serve to reinforce the W and C variants conducive to task achievement, and also the LMAN for that synergy, so that the synergy's variability can be modulated for more reward-generating actions.