Abstract
Objective: To investigate whether crossed corticospinal facilitation between arm and trunk muscles is preserved following spinal cord injury (SCI) and to elucidate these neural interactions for postural control during functional arm movements.Methods: Using transcranial magnetic stimulation (TMS) in 22 subjects with incomplete SCI motor evoked potentials (MEPs) in the erector spinae (ES) muscle were examined when the contralateral arm was at rest or performed 20% of maximal voluntary contraction (MVC) of biceps brachii (BB) or triceps brachii (TB). Trunk function was assessed with rapid shoulder flexion and forward-reaching tasks.Results: MEP amplitudes in ES were increased during elbow flexion in some subjects and this facilitatory effect was more prominent in subjects with thoracic SCI than in the subjects with cervical SCI. Those who showed the increased MEPs during elbow flexion had faster reaction times and quicker anticipatory postural adjustments of the trunk in the rapid shoulder flexion task. The onset of EMG activity in ES during the rapid shoulder flexion task correlated with the trunk excursion in forward-reaching.Conclusions: Our findings demonstrate that crossed corticospinal facilitation in the trunk muscles can be preserved after SCI and is reflected in trunk control during functional arm movements.
Highlights
Impaired voluntary control of trunk muscles is commonly seen following human spinal cord injury (SCI; Potten et al, 1999; Milosevic et al, 2015) and this can compromise activities that involve interactions between limb and trunk muscles (Kukke and Triolo, 2004; Desroches et al, 2013)
This result demonstrated that mean rectified erector spinae (ES) EMG activity was constant when the arm was at rest or performed 20% of maximal voluntary contraction (MVC) into elbow flexion and elbow extension, in agreement with our previous work in healthy subjects (Chiou et al, 2018b)
We found no difference in the level of muscle contraction exerted by biceps brachii (BB) and triceps brachii (TB) between elbow flexion (18.72 ± 9.53% BB MVC) and elbow extension (17.58 ± 9.33% TB MVC; p > 0.05)
Summary
Impaired voluntary control of trunk muscles is commonly seen following human spinal cord injury (SCI; Potten et al, 1999; Milosevic et al, 2015) and this can compromise activities that involve interactions between limb and trunk muscles (Kukke and Triolo, 2004; Desroches et al, 2013). Evidence has shown neural interactions between the pathways projecting to the arm and trunk muscles. We have recently shown that this crossed corticospinal facilitation between trunk extensor and proximal arm muscles is mediated, in part, cortically (Chiou et al, 2018b). The facilitatory effect was more prominent during elbow flexion (Chiou et al, 2018b), highlighting that the neural interactions between the arm and trunk muscles can be influenced by the task. These findings suggest that crossed facilitation may underpin functionally relevant arm-trunk interactions
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