In the left panel, each box stands for a neural population, except for P, which represents the arm and the muscles. Arrows indicate static connections, open circles show input correlation synapses, and the two colored circles show possible locations of synapses with the learning rule in Verduzco-Flores et al., 2022. In the spinal learning model the green circle connections are plastic, and the red circle connections are static. In the cortical learning model the red circle connections are plastic, whereas the green circle connections are static. In the static network all connections are static. A : afferent population. : Somatosensory cortex, modulated by afferent input. : somatosensory cortex, prescribed pattern. : population signaling the difference between and : primary motor cortex. : spinal cord. Inside the box the circles represent the excitatory () and inhibitory () interneurons, organized into six pairs. The interneurons in each pair innervate an alpha motoneuron (), each of which stimulates one of the six muscles in the arm, numbered from 0 to 5. The trios consisting of , , units are organized into agonists and antagonists, depending on whether their motoneurons cause torques in similar or opposite directions. These relations are shown in the right-side panel.