| Motor cortex (M1) neuroplasticity is of primary interest to rehabilitation scientists, as this process may underlie post-stroke recovery of movement. Of the several neurophysiologic techniques, transcranial magnetic stimulation (TMS) is the most appropriate for studying M1 plasticity. Numerous studies have used TMS, however, limited evidence exists for the reliability of this technique. In Experiment 1, we sought to establish test-retest reliability of several TMS measures of M1 organization and excitability. In Experiment 2, we used TMS to assess plasticity related to recovery of upper extremity function in stroke survivors engaged in constraint-induced (CI) movement therapy. We hypothesized that (1) TMS measures would demonstrate good test-retest reliability, and (2) that stroke survivors would demonstrate M1 plasticity following a course of CI therapy. Participants in Experiment 1 were 20 healthy volunteers. Participants in Experiment 2 were 23 individuals who were 10 months to 10.75 years post-stroke. In both experiments, the following TMS variables were investigated in two hand and two forearm muscle representations: motor map size, motor map volume, map center of gravity, recruitment curve slope, and motor threshold. Participants in both experiments were tested on two sessions separated by 2 weeks. In Experiment 2, subjects also underwent an evaluation of upper extremity function. Participants in the second experiment received CI therapy during the 2-week testing interval. The intraclass correlation coefficient was used to assess test-retest reliability. Separate t-tests were used to assess pre- to post-CI therapy differences. Association between TMS and functional outcomes was determined using the Pearson r. Group differences between high and low functioning subjects were assessed using separate ANOVAs. Noteworthy findings from Experiment 1 include generally moderate to high reliability for the TMS measures. In Experiment 2, we found significant changes in some M1 muscle representations, which were paralleled by, but not directly correlated with, functional improvements. We found generally small differences between high and low functioning groups. TMS is a reliable measure of M1 organization and excitability, and may be used to investigate activity-dependent plasticity associated with intensive upper limb training in individuals post-stroke. |
