Formation of a novel supraspinal-spinal connectome that relearns the same motor task after complete paralysis

Having observed that electrical spinal cord stimulation and training enabled four patients with paraplegia with motor complete paralysis to regain voluntary leg movement, the underlying mechanisms involved in forming the newly established supraspinal-spinal functional connectivity have become of great interest. van den Brand et al. (Science 336: 1182–1185, 2012) subsequently, demonstrated the recovery, in response to spinal electro-neuromodulation and locomotor training, of voluntary stepping of the lower limbs in rats that received a lesion that is assumed to eliminate all long-descending cortical axons that project to lumbosacral segments. Here, we used a similar spinal lesion in rats to eliminate long-descending axons to determine whether a novel, trained motor behavior triggered by a unique auditory cue learned before a spinal lesion, could recover after the lesion. Hindlimb stepping recovered 1 mo after the spinal injury, but only after 2 mo, the novel and unique audio-triggered behavior was recovered, meaning that not only was a novel connectivity formed but also further evidence suggested that this highly unique behavioral response was independent of the recovery of the circuitry that generated stepping. The unique features of the newly formed supraspinal-spinal connections that mediated the recovery of the trained behavior is consistent with a guidance mechanism(s) that are highly use dependent.