Abstract
We aimed to determine, using transcranial magnetic stimulation (TMS), the number of elicited motor evoked potentials (MEPs) that induces the highest intra- and inter-sessions reliability for the extensor carpi radialis (ECR) and first dorsal interosseus (FDI) muscles. Twelve healthy subjects participated in this study on two separate days. Single pulse magnetic stimuli were triggered with Magstim 2002 to obtain MEPs from the muscles of interest, with the subjects in a relaxed position. Reliability of MEP responses was investigated in three blocks of 5, 10 and 15 trials. The intra- and inter-session reliability of the MEPs' amplitudes and latencies were assessed using intraclass correlation coefficients (ICCs). Repeated measures ANOVA and paired t-tests revealed no significant time effect in the MEP amplitude and latency measurements (P>0.05). The ICCs indicated high intra-session reliability in the MEPs' amplitudes for the ECR and FDI muscles (0.77 to 0.99, 0.90 to 0.99, respectively) and latency (0.80 to 1.00, 0.75 to 0.97, respectively). The MEPs' amplitudes also had high inter-session reliability (0.84 to 0.97, 0.88 to 0.93, respectively), as did their latency (0.80 to 0.90, 0.75 to 0.97, respectively). Highest intra- and inter-session reliability was achieved for blocks of 10 and 15 trials. Our data suggest that intra- and inter-session comparisons should be performed using at least 10 MEPs in “combined hotspot” stimulation technique to ensure highest reliability.
Highlights
Transcranial magnetic stimulation (TMS) is a non-invasive, safe and painless technique for assessment of brain corticospinal excitability in both healthy individuals and patients with neurological conditions [1,2,3,4]
TMS-induced motor evoked potentials (MEPs) have been used as a reliable outcome measure of corticospinal excitability changes in a range of research protocols [10,11,12]
Systematic bias was evaluated by measuring the level of agreement using ANOVA or a paired t-test where appropriate
Summary
Transcranial magnetic stimulation (TMS) is a non-invasive, safe and painless technique for assessment of brain corticospinal excitability in both healthy individuals and patients with neurological conditions [1,2,3,4]. When applied over the primary motor cortex (M1) of a target muscle, TMS depolarizes nerve cells descending corticospinal pathways to contralateral muscle(s) of interest and elicits a motor response called ‘‘motor evoked potential’’ (MEP). This response can be recorded using surface electromyography (EMG) electrodes placed over the target muscle(s) [7,8,9]. TMS-induced MEPs have been used as a reliable outcome measure of corticospinal excitability changes in a range of research protocols [10,11,12]. Variation in MEP latency indicates change in the central and peripheral conduction time required for transmission of induced action potential from the M1 to the target muscle(s) [9]
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