Facilitation of the Lesioned Motor Cortex During Tonic Contraction of the Unaffected Limb Corresponds to Motor Status After Stroke

Background and Purpose: Contraction of the muscles of the unaffected hand is associated with enhanced activation of lesioned motor cortex (ie, crossed facilitation) in some individuals after stroke. However, the association between crossed facilitation and motor function status remains unclear. We investigated whether existence of crossed facilitation corresponds to motor status of the affected upper limb after stroke. Methods: Data were collected from 58 participants with unilateral stroke. The Fugl-Meyer assessment of upper extremity (FMA-UE) was used to evaluate motor status. Motor-evoked potentials (MEPs) were elicited from the abductor pollicis brevis (ABP) of the affected side under 3 conditions: rest, tonic contraction of the ABP of the unaffected side, or tonic contraction of the tibialis anterior of the unaffected side. Results: In 28 of the 58 participants, MEPs could be elicited from the affected ABP at rest; these participants also exhibited crossed facilitation during contraction on the unaffected side. Participants with MEPs at rest exhibited higher FMA-UE scores (53.04 +/- 2.59) compared with participants with absent MEP (19.83 +/- 1.60; Z = -6.21). Seven participants with no MEPs at rest had MEPs with crossed facilitation; their FMA-UE scores were higher compared with the 23 who had no ABP MEP under any condition (Z=-2.66). FMA-UE scores were positively correlated with the amount of crossed facilitation during the APB task (r = 0.68) and the tibialis anterior task (r = 0.54). Discussion and Conclusions: In some participants, MEPs in the affected hand muscle were enhanced by tonic contraction of the muscles on the unaffected side even if no MEP could be evoked at rest. The degree of crossed facilitation in the affected hand muscle was correlated with the level of motor function of the affected upper limb, and the FMA-UE score could classify the presence/absence of crossed facilitation.