Abstract
To improve our understanding of the combined transcranial magnetic stimulation (TMS) and electroencephalography (EEG) method in general, it is important to study how the dynamics of the TMS-modulated brain activity differs from the dynamics of spontaneous activity. In this paper, we introduce two quantitative measures based on EEG data, called mean state shift (MSS) and state variance (SV), for evaluating the TMS-evoked changes in the brain-state dynamics. MSS quantifies the immediate TMS-elicited change in the brain state, whereas SV shows whether the rate at which the brain state changes is modulated by TMS. We report a statistically significant increase for a period of 100–200 ms after the TMS pulse in both MSS and SV at the group level. This indicates that the TMS-modulated brain state differs from the spontaneous one. Moreover, the TMS-modulated activity is more vigorous than the natural activity.
Highlights
Combined transcranial magnetic stimulation (TMS) and electroencephalography (EEG) is able to probe the dynamics of the effective connectivity of the brain
TMS– EEG can be used to study the effect of the brain state on the dynamics of excitability: Nikulin et al (2003) showed that voluntary preparation for hand movement changes the EEG responses evoked by stimulating the primary motor cortex
Post-hoc tests revealed a significant increase in state variance (SV) during time intervals T3 and T4 compared to SVs measured at the other time intervals (Figure 2A)
Summary
Combined transcranial magnetic stimulation (TMS) and electroencephalography (EEG) is able to probe the dynamics of the effective connectivity of the brain. TMS– EEG can be used to study the effect of the brain state on the dynamics of excitability: Nikulin et al (2003) showed that voluntary preparation for hand movement changes the EEG responses evoked by stimulating the primary motor cortex. Combined TMS–EEG studies have shown that even a single TMS pulse is able to induce changes in the frequency spectrum of brain activity (Paus et al, 2001; Fuggetta et al, 2005; Rosanova et al, 2009). Using preparatory repetitive TMS (rTMS), it has been possible to modulate subsequent single-pulse TMS– EEG responses. Esser et al (2006) showed that by applying rTMS on the primary motor cortex at 5 Hz, it is possible to significantly potentiate single-pulse deflections with latencies of 15–55 ms. Frequency-tuned rhythmic TMS has been shown to selectively bias perception (Romei et al, 2010) via entrainment of ongoing oscillatory activity (Thut et al, 2011)
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