Abstract
Transcranial magnetic stimulation (TMS) has a wide range of clinical applications, and there is growing interest in neural oscillations and corticospinal excitability determined by TMS. Previous studies have shown that corticospinal excitability is influenced by fluctuations of brain oscillations in the sensorimotor region, but it is unclear whether brain network activity modulates corticospinal excitability. Here, we addressed this question by recording electroencephalography (EEG) and TMS measurements in 32 healthy individuals. The resting motor threshold (RMT) and active motor threshold (AMT) were determined as markers of corticospinal excitability. The least absolute shrinkage and selection operator (LASSO) was used to identify significant EEG metrics and then correlation analysis was performed. The analysis revealed that alpha2 power in the sensorimotor region was inversely correlated with RMT and AMT. Innovatively, graph theory was used to construct a brain network, and the relationship between the brain network and corticospinal excitability was explored. It was found that the global efficiency in the theta band was positively correlated with RMT. Additionally, the global efficiency in the alpha2 band was negatively correlated with RMT and AMT. These findings indicated that corticospinal excitability can be modulated by the power spectrum in sensorimotor regions and the global efficiency of functional networks. EEG network analysis can provide a useful supplement for studying the association between EEG oscillations and corticospinal excitability.
Highlights
Transcranial Magnetic Stimulation (TMS) induces an electric field through a time-varying magnetic field, resulting in induced electric currents and changing the action potential of nerve cells in the cerebral cortex, affecting blood circulation, metabolism, and nerve excitability in the brain (Wanalee et al, 2015)
As for global metrics, we found that the global efficiency in the theta band was positively correlated with resting motor threshold (RMT) (r = 0.374, p = 0.035), while the global efficiency in the alpha2 band was negatively correlated with RMT (ρ = −0.363, p = 0.041), showing the opposite trend
We explored the relationship between EEG oscillations and corticospinal excitability
Summary
Transcranial Magnetic Stimulation (TMS) induces an electric field through a time-varying magnetic field, resulting in induced electric currents and changing the action potential of nerve cells in the cerebral cortex, affecting blood circulation, metabolism, and nerve excitability in the brain (Wanalee et al, 2015). Some studies reported a correlation between corticospinal excitability and pre-stimulation alpha oscillation power (Sauseng et al, 2009) as well as beta oscillation power (Maki and Ilmoniemi, 2010; Hussain et al, 2019b) while others found no correlations between various EEG frequencies (Iscan et al, 2016). Sauseng et al (2009) found that the amplitude of motor evoked potentials (MEPs) is negatively correlated with the pre-stimulation alpha oscillation power, while Ogata et al (2019) reported the opposite results. These conflicting results have evoked the need for further investigation of the relationship between EEG oscillations and corticospinal excitability to obtain reliable results
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