Abstract
BackgroundThis study determined the reliability of topographic motor cortical maps and MEP characteristics in the extensor digitorum communis (EDC) evoked by single-pulse TMS among patients with chronic stroke.MethodsEach of ten patients was studied on three occasions. Measures included location of the EDC hotspot and center of gravity (COG), threshold of activation and average amplitude of the hotspot, number of active sites, map volume, and recruitment curve (RC) slope.ResultsConsistent intrahemispheric measurements were obtained for the three TMS mapping sessions for all measured variables. No statistically significant difference was observed between hemispheres for the number of active sites, COG distance or the RC slope. The magnitude and range of COG movement between sessions were similar to those reported previously with this muscle in able-bodied individuals. The average COG movement over three sessions in both hemispheres was 0.90 cm. The average COG movement in the affected hemisphere was 1.13 (± 0.08) cm, and 0.68 (± 0.04) cm) for the less affected hemisphere. However, significant interhemispheric variability was seen for the average MEP amplitude, normalized map volume, and resting motor threshold.ConclusionThe physiologic variability in some TMS measurements of EDC suggest that interpretation of TMS mapping data derived from hemiparetic patients in the chronic stage following stroke should be undertaken cautiously. Irrespective of the muscle, potential causes of variability should be resolved to accurately assess the impact of pharmacological or physical interventions on cortical organization as measured by TMS among patients with stroke.
Highlights
This study determined the reliability of topographic motor cortical maps and motor evoked potential (MEP) characteristics in the extensor digitorum communis (EDC) evoked by single-pulse Transcranial Magnetic Stimulation (TMS) among patients with chronic stroke
The scalp overlying the motor cortex was stimulated at 110% of motor threshold, while recording from EDC
The resting motor threshold (RMT) in the affected hemisphere had a minimum value of 43% and maximum value of 100%
Summary
This study determined the reliability of topographic motor cortical maps and MEP characteristics in the extensor digitorum communis (EDC) evoked by single-pulse TMS among patients with chronic stroke. TMS has been used to explore mechanisms underlying both spontaneous and therapy-induced post-stroke motor recovery. In this context, most interventional studies have not considered intra-subject variability of TMS maps prior to the provision of a therapy, implying that cortical changes are attributable to the intervention. Our laboratory recently demonstrated significant variability within ablebodied, right hand dominant participants across sessions and between hemispheres, for distance between the lowest resting motor threshold locations for a muscle (hotspot), center of gravity distance, and normalized map volume TMS parameters when mapping the extensor digitorum communis (EDC) muscle [5]. Wasserman et al (2002) found no systematic changes in resting and active motor evoked potential (MEP) thresholds among 19 women across three sessions
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