Impaired transmission in the corticospinal tract and gait disability in spinal cord injured 1 persons 2 3

32 33 Rehabilitation following spinal cord injury is likely to depend on recovery of 34 corticospinal systems. Here we investigate whether transmission in the corticospinal tract 35 may explain foot drop (inability to dorsiflex ankle) in persons with spinal cord lesion. 36 The study was performed in 24 persons with incomplete spinal cord lesion (C1 to L1) and 37 15 healthy controls. Coherence in the 10-20 Hz frequency band between paired tibialis 38 anterior muscle (TA) electromyographic recordings obtained in the swing phase of 39 walking, which is taken as a measure of motor unit synchronization, was significantly 40 correlated with the degree of foot drop, as measured by toe elevation and ankle angle 41 excursion in the first part of swing. Transcranial magnetic stimulation (TMS) was used 42 to elicit motor evoked potentials (MEPs) in the TA. The amplitude of the MEPs at rest 43 and their latency during contraction were correlated to the degree of foot drop. Spinal 44 cord injured participants who exhibited a large foot drop had little or no MEP at rest in 45 the TA muscle and had little or no coherence in the same muscle during walking. Gait 46 speed was correlated to foot drop, and was the lowest in participants with no MEP at rest. 47 The data confirm that transmission in the corticospinal tract is of importance for lifting 48 the foot during the swing phase of human gait. 49 50