Spinal neuronal dysfunction after stroke

Central nervous system lesions, such as stroke or spinal cord injury (SCI), are followed by both cortical and spinal neuronal reorganization. In a severe chronic SCI a spinal neuronal dysfunction develops which is reflected in an exhaustion of leg muscle electromyographic (EMG) activity during assisted locomotion and a change in the dominance from an early to a late polysynaptic spinal reflex (SR) component. The aim of this study was to investigate the course of spinal neuronal function after a severe stroke, i.e., a unilateral deprivation of supraspinal input. In 30 hemiparetic stroke subjects locomotor and SR behavior were assessed. SR responses in the tibialis anterior muscle were evoked by non-noxious tibial nerve stimulation on both, the affected and the unaffected leg. In nine stroke subjects EMG activity of the leg muscles was recorded during assisted locomotion. In a similar way to SCI subjects, in severely affected chronic (>12 months post-incidence) stroke subjects a late SR component was prominent in the affected leg, while an early one dominated in the unaffected leg. The late SR component correlated with muscle paresis (rho=0.714) and walking ability (rho=0.493). In contrast to SCI subjects, no exhaustion of the EMG activity was observed in the affected leg muscles during prolonged assisted locomotion. It is concluded that spinal neuronal circuits undergo functional changes also after a stroke which have common as well as divergent features compared to SCI subjects. As a consequence, different rehabilitative strategies might be required.