Proceedings of The Physiological Society
University College London December 2005 (2006) Proc Physiol Soc 1, C19
Improvements in locomotor function in subjects with incomplete spinal cord injury are associated with changes in inter-muscular coherence
Norton, Jonathan A; Gorassini, Monica A;
1. Department of Biomedical Engineering & Centre for Neuroscience, University of Alberta, Edmonton, AB, Canada.
Figure 1. The mean area of coherence in 2 frequency bands (5-18 Hz: left bars and 24-40 Hz: right bars) before and after training in subjects who responded to treadmill training (Resp.) and those who did not (Non Resp.). The mean area of coherence in 24-40 Hz band was significantly lower in the non-responders compared to the responders before training and significantly greater after training compared to before in the responders. * P < 0.05 ** P < 0.01. Error bars represent standard error.
Treadmill training with partial body-weight support improves locomotor function in humans with incomplete spinal cord injuries (iSCI). A recent study has shown that subjects who improve their locomotor ability also demonstrate increases in corticospinal tract function as assessed by transcranial magnetic stimulation (TMS) (Thomas & Gorassini, 2005). In the present study we examined if increases in inter-muscular coherence recorded during walking, especially in the 24-40 Hz band which may indicate common cortical drive (Mima & Hallet, 1999), were also associated with locomotor improvement. Coherence was measured between the hamstrings and quadriceps muscles during the stance phase of walking. Coherence was measured before and after 3-5 months of intensive treadmill training in 12 subjects with iSCI. In subjects who demonstrated functional improvements in walking (termed responders), there was also an increase in the level of coherence in the 24-40 Hz frequency band (p<0.05, paired t test, Fig. 1). In subjects who did not improve in their locomotor ability (non-responders), coherence in the 24-40 Hz frequency band was low and did not change after training. There were no significant changes in coherence values in the range of frequencies from 5-18 Hz (spinal band) in both groups. Increased coherence in the 24-40 Hz band after training may represent increased corticospinal drive to the musculature during walking. Interestingly, in 8 subjects who also participated in TMS experiments, the amount of increase in 24-40 Hz coherence was significantly related to the amount of increase in evoked muscle responses to TMS. We propose that measures of inter-muscular coherence can provide information concerning the contribution of spared corticospinal pathways in mediating motor recovery following rehabilitation.
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