This Week in The Journal

To generate a movement, spinal motor neurons must receive the correct inputs from the brain.This sounds simple enough, but it remains unclear how neurons in the brain can accurately target such a large quantity of motor neurons with high precision.Rossato et al. explored this in their study in this issue.In a group of male participants, they assessed how well motor units (defined as a motor neuron and all the skeletal fibers innervated by that neuron) could be controlled independently.To do this, they used an online program that presents firing rates as visual feedback while participants perform different muscle contractions.They found that individual motor units could not be controlled independently and that they were segregated into synergistic groups.These findings suggest that there are common synaptic inputs from the cortex onto groups of motor neurons and not individual motor neurons, which supports the "low-dimensional movement control" hypothesis in the field.