Figure 1.

Anatomical experiments and recording conditions. A, The 3D anatomical reconstruction of corticospinal and motor neuron locations. Density and location of retrogradely traced corticospinal neurons following FastBlue injections into lumbar segments. Red dots represent average electrode locations. B, Density and location of retrogradely traced motor neurons following Fluorogold injections into hindlimb muscles. The tibialis anterior served as an anatomical landmark to align tracing from multiple rats. C, The 3D representation of the 32 electrode array inserted into layer V of cortical territories projecting to lumbar segments. The photograph represents the location of two electrode tips in the vicinity of corticospinal neurons projecting to lumbar segments from a single rat. D, EMG activity recorded from right hindlimb muscles during locomotion. Twelve high-resolution cameras monitored the 3D displacements of reflective markers to measure bilateral limb and head kinematics. Single-unit and multiunit activity was extracted from extracellular recordings in the left cortex. Each panel represents an electrode. A distinct color represents each sorted unit. Ground reaction forces were monitored during overground gait initiation. E, Characteristics of the locomotor paradigms; rung spacing on the ladder was irregular.