Ipsilateral Motor Pathways and Transcallosal Inhibition During Lower Limb Movement After Stroke

Background Stroke rehabilitation may be improved with a better understanding of the contribution of ipsilateral motor pathways to the paretic limb and alterations in transcallosal inhibition. Few studies have evaluated these factors during dynamic, bilateral lower limb movements, and it is unclear whether they relate to functional outcomes. Objective Determine if lower limb ipsilateral excitability and transcallosal inhibition after stroke depend on target limb, task, or number of limbs involved, and whether these factors are related to clinical measures. Methods In 29 individuals with stroke, ipsilateral and contralateral responses to transcranial magnetic stimulation were measured in the paretic and nonparetic tibialis anterior during dynamic (unilateral or bilateral ankle dorsiflexion/plantarflexion) and isometric (unilateral dorsiflexion) conditions. Relative ipsilateral excitability and transcallosal inhibition were assessed. Fugl-Meyer, ankle movement accuracy, and walking characteristics were assessed. Results Relative ipsilateral excitability was greater during dynamic than isometric conditions in the paretic limb (P ≤ .02) and greater in the paretic than the nonparetic limb during dynamic conditions (P ≤ .004). Transcallosal inhibition was greater in the ipsilesional than contralesional hemisphere (P = .002) and during dynamic than isometric conditions (P = .03). Greater ipsilesional transcallosal inhibition was correlated with better ankle movement accuracy (R2 = 0.18, P = .04). Greater contralateral excitability to the nonparetic limb was correlated with improved walking symmetry (R2 = 0.19, P = .03). Conclusions Ipsilateral pathways have increased excitability to the paretic limb, particularly during dynamic tasks. Transcallosal inhibition is greater in the ipsilesional than contralesional hemisphere and during dynamic than isometric tasks. Ipsilateral pathways and transcallosal inhibition may influence walking asymmetry and ankle movement accuracy.