Losing control

Neurologic examination after focal motor injury tends to focus on weakness rather than control. One reason for this may be the implicit assumption that weakness precludes control. Most neurologists, however, are familiar with the common bedside finding in patients with hemiparesis after stroke: they can squeeze your hand with surprising force but cannot make individuated finger movements. This dissociation is also seen when comparing the effect of a unilateral hemispheric stroke on motor performance in the ipsilateral arm; strength is unaffected but skilled movements are impaired.¹ The separation between control of movement and of isometric force has a long tradition in the design of robot arms² and psychophysical evidence suggests that these 2 types of control may be partitioned in the brain.³

In this issue of Neurology®, van Hedel et al.⁴ shed further anatomic light on the strength/skill dissociation by comparing leg motor deficits in patients with incomplete spinal cord injury (iSCI) and patients with unilateral hemispheric stroke. The main hypothesis was that these 2 patient groups would show differential skill levels despite comparable degrees of weakness. The hypothesis was based on the idea that in iSCI, all descending pathways from the brain to the spinal cord segments below the lesion are affected in the …