Figure 7. A compositional neural code may facilitate the transfer of motor skills across limbs.

(A) We speculate that premotor cortex (the site of our arrays) might receive input from upstream areas in the form of a “compositional” representation of movement where the limb is specified somewhat independently of the motion details. In this example, activity in the “laterality” and “arm vs. leg” input streams specify which of the four limbs should move, and activity in the “wrist/ankle motion pattern” input stream specifies the motion that should be performed (at a wrist or ankle joint). Premotor cortex and primary motor cortex would then convert this representation into limb-specific muscle patterns to achieve a desired joint motion.

(B) The same motion pattern could be transferred to any other wrist or ankle by changing activity only in the “laterality” and “arm vs. leg” dimensions, achieving immediate transfer without requiring relearning.

See Figure S7 for a concrete implementation of this hypothesis in a neural network model.