Characterizing differential poststroke corticomotor drive to the dorsi- and plantarflexor muscles during resting and volitional muscle activation

Abstract

Imbalance of corticomotor excitability between the paretic and nonparetic limbs has been associated with the extent of upper extremity motor recovery poststroke, is greatly influenced by specific testing conditions such as the presence or absence of volitional muscle activation, and may vary across muscle groups. However, despite its clinical importance, poststroke corticomotor drive to lower extremity muscles has not been thoroughly investigated. Additionally, whereas conventional gait rehabilitation strategies for stroke survivors focus on paretic limb foot drop and dorsiflexion impairments, most contemporary literature has indicated that paretic limb propulsion and plantarflexion impairments are the most significant limiters to poststroke walking function. The purpose of this study was to compare corticomotor excitability of the dorsi- and plantarflexor muscles during resting and active conditions in individuals with good and poor poststroke walking recovery and in neurologically intact controls. We found that plantarflexor muscles showed reduced corticomotor symmetry between paretic and nonparetic limbs compared with dorsiflexor muscles in individuals with poor poststroke walking recovery during active muscle contraction but not during rest. Reduced plantarflexor corticomotor symmetry during active muscle contraction was a result of reduced corticomotor drive to the paretic muscles and enhanced corticomotor drive to the nonparetic muscles compared with the neurologically intact controls. These results demonstrate that atypical corticomotor drive exists in both the paretic and nonparetic lower limbs and implicate greater severity of corticomotor impairments to plantarflexor vs. dorsiflexor muscles during muscle activation in stroke survivors with poor walking recovery. NEW & NOTEWORTHY The present study observed that lower-limb corticomotor asymmetry resulted from both reduced paretic and enhanced nonparetic limb corticomotor excitability compared with neurologically intact controls. The most asymmetrical corticomotor drive was observed in the plantarflexor muscles of individuals with poor poststroke walking recovery. This suggests that neural function of dorsi- and plantarflexor muscles in both paretic and nonparetic limbs may play a role in poststroke walking function, which may have important implications when developing targeted poststroke rehabilitation programs to improve walking ability.