Figure 3.

The influence of internal motor copy circuitry during rehabilitation. (A) Schematic illustration depicting the internal motor copy, a cerebellar loop that makes a forward prediction of sensory input. It is thought to be primarily performed in the cerebellum and, to a lesser extent, within local spinal circuits. Predictions are compared (and respond) to incoming proprioceptive information to adjust motor actions in real-time before the completion of the movement. Supraspinal networks, including the cortical spinal tract (CST, purple), reticulospinal tract (ReST, blue), and rubrospinal tract (not shown) relay planned motor information to the cerebellum to generate the internal motor copy. Multiple internal motor copies are relayed to the cerebellar loop via the Lateral Reticular Nucleus. Simultaneously, sensory information from the periphery is relayed to the cerebellum via spinocerebellar tracts. Comparative analyses are performed within this cerebellar loop to communicate what the intended motor command accomplished. Supraspinal fibers converge onto interneurons (INs, black), including (PNs, green), to indirectly excite motoneurons. (B) With lesion, fibers from the reticulospinal tract (ReST, blue) may relay cortical commands, as the internal motor copy is unaffected by the lesion and spared and injured PNs can dynamically reorganize after SCI. With EES, input from the ReST spatiotemporally combines with increased activity of group Ia afferents to achieve supra-threshold activation of interneurons as well as indirectly activating motoneurons (MNs, red and orange).