The motor cortex drives the muscles during walking in human subjects

Abstract

Key points• It is often assumed that automatic movements such as walking require little conscious attention and it has therefore been argued that these movements require little cortical control.• In humans, however, the gait function is often heavily impaired or completely lost following cortical lesions such as stroke.• In this study we investigated synchrony between cortical signals recorded with electroencephalography (EEG) and electromyographic signals (EMG activity) recorded from the tibialis anterior muscle (TA) during walking.• We found evidence of synchrony in the frequency domain (coherence) between the primary motor cortex and the TA muscle indicating a cortical involvement in human gait function.• This finding underpins the importance of restoration of the activity and connectivity between the motor cortex and the spinal cord in the recovery of gait function in patients with damage of the central nervous system.Abstract Indirect evidence that the motor cortex and the corticospinal tract contribute to the control of walking in human subjects has been provided in previous studies. In the present study we used coherence analysis of the coupling between EEG and EMG from active leg muscles during human walking to address if activity arising in the motor cortex contributes to the muscle activity during gait. Nine healthy human subjects walked on a treadmill at a speed of 3.5-4 km h −1 . Seven of the subjects in addition walked at a speed of 1 km h −1 . Significant coupling between EEG recordings over the leg motor area and EMG from the anterior tibial muscle was found in the frequency band 24-40 Hz prior to heel strike during the swing phase of walking. This signifies that rhythmic cortical activity in the 24-40 Hz frequency band is transmitted via the corticospinal tract to the active muscles during walking. These findings demonstrate that the motor cortex and corticospinal tract contribute directly to the muscle activity observed in steady-state treadmill walking.

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

“…59 As noted in a recent systematic review, however, the clinical usefulness of these approaches for prediction of outcomes and forecasting responsiveness to training has yet to be established. 149 To justify the greater time and resource requirements needed to acquire these state-of-the-art measurements, in order to have true value as biomarkers for recovery, they will need to provide a more accurate picture of future walking status than do prediction rules based on clinical measures.…”

“…59 The role of the motor cortex in human walking has been elucidated by studies in humans showing that: (1) subthreshold transcranial magnetic stimulation (TMS) to activate inhibitory interneurons in the motor cortex suppresses the locomotor EMG in the ankle dorsi -and plantar flexor muscles, 61 (2) suprathreshold TMS activates dorsiflexors to the same extent as during volitional contractions in sitting, 62 and (3) electroencephalographic (EEG)-EMG coherence shows synchrony in the frequency domain between the primary motor cortex and the dorsiflexors during walking. 59 Most of the evidence related to corticomotor control of walking in humans has focused on the dorsiflexor muscles, in which there is step-to-step modulation of muscle activity during level overground walking (or at least a constant drive to facilitate spinal circuitry). 59,61 The role of the motor cortex in other locomotor muscles remains to be elucidated, as does a potentially modified role of supraspinal inputs following injury wherein walking speeds are slower and the task of walking requires more cognitive attention.…”

“…attention, with studies showing direct contributions to the ankle dorsiflexors, 59,60 including activation on a step-to-step basis. 59 The role of the motor cortex in human walking has been elucidated by studies in humans showing that: (1) subthreshold transcranial magnetic stimulation (TMS) to activate inhibitory interneurons in the motor cortex suppresses the locomotor EMG in the ankle dorsi -and plantar flexor muscles, 61 (2) suprathreshold TMS activates dorsiflexors to the same extent as during volitional contractions in sitting, 62 and (3) electroencephalographic (EEG)-EMG coherence shows synchrony in the frequency domain between the primary motor cortex and the dorsiflexors during walking.…”

“…59 Most of the evidence related to corticomotor control of walking in humans has focused on the dorsiflexor muscles, in which there is step-to-step modulation of muscle activity during level overground walking (or at least a constant drive to facilitate spinal circuitry). 59,61 The role of the motor cortex in other locomotor muscles remains to be elucidated, as does a potentially modified role of supraspinal inputs following injury wherein walking speeds are slower and the task of walking requires more cognitive attention. 63 Step initiation is another critical aspect of locomotor function that appears to be under supraspinal control.…”

Identification of connectivity in human motor control: exciting the afferent pathways

“…Previous studies did not show a clear effect of walking speed on EMG-EMG (Hansen et al, 2005;den Otter et al, 2004) or EEG-EMG (Petersen et al, 2012) coherence. In accordance with these studies we also observed no influence of walking speed on the coherence variables.…”