Increases in Corticospinal Tract Function by Treadmill Training After Incomplete Spinal Cord Injury

Abstract

Thomas, Sarah L. and Monica A. Gorassini. Increases in corticospinal tract function by treadmill training after incomplete spinal cord injury. J Neurophysiol 94: 2844 -2855, 2005 First published July 6 2005. doi:10.1152/jn.00532.2005. In this study, we examined if several months of intensive locomotor training increases the function of spared corticospinal tract pathways after chronic spinal cord injury (SCI) in association with the recovery of locomotor function. Transcranial magnetic stimulation (TMS) at incrementing levels of intensity was applied over the motor cortex supplying either the tibialis anterior or vastus lateralis muscles, and the resulting peak-to-peak amplitude of the motor-evoked potentials (MEPs) were measured to obtain a recruitment curve both before and after training. In the majority of subjects (7/8), 3-5 mo of daily intensive training increased the responses to TMS in at least one of the leg muscles tested (9/13). On average, across all muscles tested MEP max , which was evoked at high stimulation intensities, increased by 46% and MEP h , which was evoked at intermediate stimulation intensities, increased by 45% (both significantly different from 0), indicating an increase in corticospinal tract connectivity from training. The slope of the sigmoid function fit to the recruitment curve increased by 24% after training (significantly different), indicating an expansion and/or increased excitability of corticospinal circuits supplying muscles to the lower leg. We also observed that the average duration of the silent period measured at MEP max increased after training from 130 to 178 ms, suggesting that training had effects on cortical circuits thought to mediate this longlasting inhibition. The percentage increase in MEP max was positively and significantly correlated to the degree of locomotor recovery as assessed by the WISCI II score, the distance a subject could walk in 6 min, and the amplitude of the locomotor EMG activity, suggesting that the corticospinal tract, in part, mediated the functional locomotor recovery produced from training.

The Effect of Exercise Training in Improving Motor Performance and Corticomotor Excitability in People With Early Parkinson's Disease

“…This is not the first report of postintervention and specifically post treadmill training effects on corticomotor excitability using TMS in people with neuropathology. Changes in corticomotor excitability and associated improvements in walking function were found after intensive treadmill training both in people with spinal cord injury 57,58 and stroke. 59 However, to our knowledge, this is the first demonstration of exercise-induced changes in corticomotor excitability using TMS in individuals with PD, a progressive neurologic disorder.…”

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

“…86 A small imaging study with four subjects indicated increased activation in the cortical sensorimotor and cerebellar regions after locomotor training in both subacute and chronic, motor-incomplete SCI. 87 In a case report of an individual with chronic, motorincomplete SCI, locomotor training that emphasized feedback-error learning was associated with increases in somatosensory and corticospinal excitability, as well as radiographic evidence of increased corticospinal connectivity.…”

Spinal Cord Injury: Time to Move?

“…What are the mechanisms of such improvements? Using motor evoked potentials induced by transcranial magnetic stimulation as an indicator of excitability changes of the corticospinal pathway, it was found that, after a period of treadmill locomotor training, corticospinal responses (Thomas and Gorassini, 2005) are increased and cortical-dependent muscle unit coherence is increased, suggesting a major role of the cortex in human rehabilitation. Although such supraspinal participation is certainly sine qua none to regain voluntary locomotor control (Yang and Gorassini, 2006), intrinsic spinal mechanisms are probably also of crucial importance in the proper expression of locomotion in humans as was shown in the cat (Barrière et al, 2007).…”