Extended Data Fig. 9 |. Simulation of SCS biophysics in a severe lesion.

a, Root-mean square (RMS) of the difference between the motoneuron firing rate pre- vs postlesion for all simulated SCS parameters in a severe lesion (same as in Fig. 4j, but with a system with 11 supraspinal fibers). As with isometric force simulations in Fig. 7b, there is a shrinking of the voluntary movement regime where small task errors occur for a very restrained combination of SCS parameters. The gray lines in the heatmap indicate the voluntary movement regime for this severe lesion (Fig. 7b). b, Simulation of the normalized force and motoneuron pool firing rate during phasic activation of supraspinal fibers (2 seconds active, 2 seconds inactive) and continuous SCS at parameters belonging to the involuntary movement regime. Residual supraspinal fibers sculpt SCS drive ro produce functional motoneuron activity. Motoneurons firing is inhibited by the phasic activation of residual supraspinal fibers (red). c, Same as b, but SCS initiates 500 ms after the initiation of supraspinal fibers (red). Motoneurons now fire only coinciding with temporal activation of SCS.