Sensory contributions to motor deficits after stroke: What is the role of the unaffected cortex in motor recovery?

Sensorimotor deficits after stroke are commonly associated with increased activation in a number of cortical areas in the non-affected hemisphere, including primary motor and sensory cortex. Constraining the unaffected arm in individuals with stroke stimulates recovery in the use of the stroke affected arm, perhaps by reestablishing the balance of excitability between affected and non-affected cortices controlling each arm. However, the specific physiological mechanisms that follow decreasing unaffected arm use are not completely understood. Immobilization of the unaffected limb in stroke patients, by ischemia or anesthetic numbing, results in transient increases in motor function of the hemiparetic upper limb. The benefit of peripheral numbing may work through decreased proprioceptive and tactile inputs to sensory cortex which in turn diminish the overall excitability of the contralesional motor areas; the net result is a reduction in transcallosal inhibition on the affected cortex. However, beyond these preliminary findings, the role of the unaffected sensory cortex in movement deficits after stroke remains largely uncharacterized. Dr. Sean Meehan is investigating whether reducing the efficacy of proprioceptive and tactile inputs from the non-affected hand at the level of sensory cortex using continuous theta burst (cTBS), a variant of transcranial magnetic stimulation (TMS), can result not only in transient improvements in motor performance in the hemiparetic arm but also longer lasting functional changes associated with motor learning. The results of Dr. Meehan’s research may encourage rehabilitative strategies that target both the sensory and motor causes of movement deficits. The addition of sensory specific rehabilitative techniques may allow for even greater increases in function than are currently possible in individuals in the chronic phase of stroke. This line of research offers a promising new avenue for advances in the conceptualization of stroke rehabilitation.