Atypical cortical drive during activation of the paretic and nonparetic tibialis anterior is related to gait deficits in chronic stroke

Objective: The role of cortical drive in stroke recovery for the lower extremity remains ambiguous. The purpose of this study was to investigate the relationship between cortical drive and gait speed in a group of stroke survivors. Methods: Eighteen individuals with stroke were dichotomized into fast or slow walking groups. Transcranial magnetic stimulation (TMS) was used to collect motor evoked potentials (MEPs) from the tibialis anterior of each lower extremity during rest, paretic muscle contractions, and nonparetic muscle contractions. An asymmetry-index (AI) was calculated using motor thresholds and compared between groups. The average MEP of the paretic leg during TMS at maximal intensity (MEP₁₀₀) for each condition was compared within and between groups. Results: A significant positive correlation was found between AI and walking speed. Slow-walkers had greater MEP₁₀₀s during the nonparetic contraction than during the paretic contraction or rest conditions. In contrast, fast-walkers had greatest MEP₁₀₀s during the paretic contraction. Conclusions: Alterations in the balance of corticomotor excitability occur in the lower extremity of individuals with poor motor recovery post-stroke. This atypical cortical drive is dependent on activation of the unaffected hemisphere and contraction of the nonparetic leg. Significance: Understanding mechanisms underlying motor function can help to identify specific patient deficits that impair function.