Changes in Cortically Related Intermuscular Coherence Accompanying Improvements in Locomotor Skills in Incomplete Spinal Cord Injury

Abstract

. Changes in cortically related intermuscular coherence accompanying improvements in locomotor skills in incomplete spinal cord injury. J Neurophysiol 95: 2580 -2589, 2006. First published January 11, 2006 doi:10.1152/jn.01289.2005. In human spinal cord injury, the neuronal mechanisms mediating the improvement of locomotor function in response to intensive treadmill training are not well understood. In this study, we examined if such recovery is mediated, in part, by increases in residual corticospinal drive to muscles of the leg during walking. To do this, we measured the coherence of electromyogram (EMG) activity between two antagonist muscles (intermuscular coherence), specifically at frequencies between 24 and 40 Hz, which is thought to indicate common drive to two muscles from corticospinal inputs. In 12 subjects with incomplete spinal cord injury, intermuscular coherence was measured between hamstrings and vastus lateralis EMG that was activated during walking on a motorized treadmill. Before training, appreciable coherence in the 24 -40 Hz frequency band was only present in subjects with moderate volitional motor strength in their leg muscles (n ϭ 8 subjects) compared with subjects with little or no leg muscle strength (n ϭ 4 subjects), reconfirming that 24 -40 Hz frequency coherence is likely mediated by common supraspinal inputs. After training, increases in 24 -40 Hz coherence only occurred in the eight subjects with moderate leg muscle strength who also exhibited improvements in locomotor recovery as assessed by the 21 point WISCI II scale (termed responders). In contrast, development of intermuscular coherence in the 24 -40 Hz frequency band did not occur in the four subjects with absent or weak muscle strength. These subjects also did not improve in their locomotor ability as reflected in unchanging WISCI II scores (termed nonresponders). Lower-frequency coherence (5-18 Hz), which is thought to contain common drive from spinal inputs, did not change in either group. In a subset of subjects that were previously assessed with transcranial magnetic stimulation (TMS) before and after training (n ϭ 5 responders and 3 nonresponders), there was a significant and positive relationship between increases in 24 -40 Hz coherence and increases in evoked muscle responses to TMS of the primary motor cortex. Taken together, increases in higher-frequency EMG coherence in subjects with residual voluntary muscle strength and its parallel relation to changes in TMS-evoked responses provides further evidence that improvements in locomotor function from treadmill training are mediated, in part, by increases in corticospinal drive to muscles of the leg during walking.

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.…”

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

“…Care should be taken when comparing the area of coherence from studies or conditions with different amounts of segments available and/or used in the analysis. Especially when the area of coherence is used to assess the effect of rehabilitation interventions, there is a considerable chance that individuals are able to walk for a longer time post compared to pre intervention (Norton and Gorassini, 2006). The larger number of available segments for analysis would introduce a bias towards finding an increase in the area of coherence.…”

“…Early studies explored the cortical involvement in the control of walking (Hansen et al, 2001;Halliday et al, 2003;Petersen et al, 2010). More clinically oriented studies showed that the EMG-EMG coherence in the beta band in patients with motor deficits resulting from stroke (Bo Nielsen et al, 2008) or spinal cord injury (Barthélemy et al, 2010;Hansen et al, 2005;Norton and Gorassini, 2006) is decreased. These decreases indicate that beta-band EMG-EMG coherence depends largely on the integrity of the corticospinal tract.…”

“…Furthermore, quantification of EMG-EMG coherence has been used to monitor corticospinal drive as a result of a gait rehabilitation intervention. Norton and Gorassini (2006) demonstrated that changes in locomotor function in spinal cord injury subjects after an extensive treadmill training program were accompanied by increases in corticospinal drive. This was considered to reflect neuroplasticity.…”

“…A commonly used derived variable is the area of coherence (Coh area ) (Barthélemy et al, 2010;Norton and Gorassini, 2006;Power et al, 2006) which is the area under the coherence spectrum dwelling above the 95% confidence limit within a certain frequency band. Another typical variable is the peak coherence (Coh peak ) which is the peak value of the spectrum within a certain frequency band (Petersen et al, 2010;Perez et al, 2006).…”