Reduction of Common Synaptic Drive to Ankle Dorsiflexor Motoneurons During Walking in Patients With Spinal Cord Lesion

Abstract

It is possible to obtain information about the synaptic drive to motoneurons during walking by analyzing motor-unit coupling in the time and frequency domains. The purpose of the present study was to compare motor-unit coupling during walking in healthy subjects and patients with incomplete spinal cord lesion to obtain evidence of differences in the motoneuronal drive that result from the lesion. Such information is of importance for development of new strategies for gait restoration. Twenty patients with incomplete spinal cord lesion (SCL) participated in the study. Control experiments were performed in 11 healthy subjects. In all healthy subjects, short-term synchronization was evident in the discharge of tibialis anterior (TA) motor units during the swing phase of treadmill walking. This was identified from the presence of a narrow central peak in cumulant densities constructed from paired EMG recordings and from the presence of significant coherence between these signals in the 10- to 20-Hz band. Such indicators of short-term synchrony were either absent or very small in the patient group. The relationship between the amount of short-term synchrony and the magnitude of the 10- to 20-Hz coherence in the patients is discussed in relation to gait ability. It is suggested that supraspinal drive to the spinal cord is responsible for short-term synchrony and coherence in the 10- to 20-Hz frequency band during walking in healthy subjects. Absence or reduction of these features may serve as physiological markers of impaired supraspinal control of gait in SCL patients. Such markers could have diagnostic and prognostic value in relation to the recovery of locomotion in patients with central motor lesions.

Single joint perturbation during gait: Preserved compensatory response pattern in spinal cord injured subjects

“…al., 1989) This is likely to be particularly true for the TA muscle which is thought to be under a greater cortical control than is the GM (Schubert et al, 1997;. This observation is also consistent with recent findings that there is reduced synaptic drive to the TA during walking in SCI individuals compared to non-disabled subjects (Hansen et al, 2005).…”

Supraspinal Control Predicts Locomotor Function and Forecasts Responsiveness to Training after Spinal Cord Injury

“…117 This premise has been tested in an operant conditioning training program in humans targeting improved volitional control of ankle dorsiflexion. 70 The focus on ankle dorsiflexion arose from evidence that corticospinal drive to the ankle dorsiflexors is impaired in persons with SCI, 118 and control of ankle dorsiflexion represents a physiologic assay of locomotor control. 119 In comparison with a training intervention targeting reduction of reflex amplitude in the ankle plantar flexors, training to increase volitional control of dorsiflexors was associated with meaningful effects in a greater number of outcome measures including walking speed and step height.…”

Usefulness of intermuscular coherence and cumulant analysis in the diagnosis of postural tremor

“…We chose cumulant density In some data sets, cumulant analysis did not reveal any significant correlation structure between EMG bursts. In addition, when data was contaminated by EMG cross-talk as identified by the combination of a sharp narrow central peak (<10 ms) in the cumulant, broadband coherence (>0.5 above 30 Hz) and flat phase (Farmer et al 1993;Hansen et al 2005), the related data sets were excluded from further analysis.…”