Spinal inhibition of descending command to soleus motoneurons is removed prior to dorsiflexion

Non-technical summary: The coordination of antagonistic muscle activity starts well in advance of the onset of voluntary movement. We recently demonstrated that antagonist muscle responses evoked by stimulation of the brain were increased prior to voluntary contraction at the ankle. Although our data indicated that this was explained by activation of a subcortical motor program, the neural pathways involved are unknown. Here we probe the transmission in the underlying neuronal networks by peripheral nerve stimulation in order to investigate the neural pathways responsible for this facilitation of antagonist muscle responses. We demonstrate that this stimulation produces a spinal inhibition of the antagonist muscle responses, which is removed prior to voluntary contraction. We propose that the removal of this inhibition might explain the increased antagonist muscle responses prior to voluntary contraction at the ankle. This mechanism might enable the direction of movement to be changed quickly during functional motor tasks such as dribbling.