Abstract
The paired-pulse transcranial magnetic stimulation (TMS) is an effective and non-invasive way to assess cortical excitability. The threshold tracking TMS (TT-TMS) was developed to overcome the variability in motor evocated potentials (MEP) amplitude caused by traditional TMS methods. Recently, TT-TMS has been widely used as a neurophysiological biomarker for upper motor neuron involvement. To date, the effect of age and gender has been assessed in healthy subjects while the influence of genetic backgrounds have not been well documented. However, previous study revealed that Chinese subjects tended to have significantly different TMS parameters compared with Caucasian subjects utilizing a constant TMS protocol. As such, we investigate effects of genetic backgrounds on cortical excitability by TT-TMS techniques. Cortical excitability was evaluated on twenty-five Chinese healthy subjects (10 males, 15 females; mean age = 28.80 ± 8.16 years) and eighteen matched Caucasian healthy controls (10 males, 8 females; mean age = 32.67 ± 8.49 years) by recording from the dominant abductor pollicis brevis (APB) muscle. A paired-pulse protocol was used to measure the short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF). MEP and cortical silent period (CSP) duration were compared between two groups by single-pulse TMS. Compared with Caucasian people, Chinese subjects exhibited an increased RMT (Chinese 59.04 ± 8.89%; Caucasian 48.04 ± 10.47%[mean ± SE], p = 0.001). Although Chinese group had a trend of decreased cortical inhibition with a reduced average SICI (Chinese 9.03 ± 9.95%; Caucasian 12.23 ± 8.35%, p = 0.273) and increased ICF (Chinese 0.003 ± 6.68%; Caucasian −0.17 ± 5.95%, p = 0.933) the differences were not significant. In terms of single-pulse TMS, there were no significant differences between two groups in CSP duration(Chinese 173.46 ± 38.54 ms; Caucasian 184.76 ± 36.7 ms, p = 0.339) and MEP/CMAP ratio (Chinese 22.85 ± 14.03%; Caucasian 22.78 ± 15.00%, p = 0.99). In this study, TT-TMS is proven to be a reliable method to assess cortical function in Chinese subjects. Of further relevance, these findings also provide evidence for interpreting the effects of genetic backgrounds on TMS variables in clinical practice.
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