Abstract
Transcranial magnetic stimulation (TMS) has often been used in conjunction with electroencephalography (EEG), which is effective for the direct demonstration of cortical reactivity and corticocortical connectivity during cognitive tasks through the spatio-temporal pattern of long-latency TMS-evoked potentials (TEPs). However, it remains unclear what pattern is associated with the inhibition of a planned motor response. Therefore, we performed TMS-EEG recording during a go/stop task, in which participants were instructed to click a computer mouse with a right index finger when an indicator that was moving with a constant velocity reached a target (go trial) or to avoid the click when the indicator randomly stopped just before it reached the target (stop trial). Single-pulse TMS to the left (contralateral) or right (ipsilateral) motor cortex was applied 500 ms before or just at the target time. TEPs related to motor execution and inhibition were obtained by subtractions between averaged EEG waveforms with and without TMS. As a result, in TEPs induced by both contralateral and ipsilateral TMS, small oscillations were followed by a prominent negative deflection around the TMS site peaking at approximately 100 ms post-TMS (N100), and a less pronounced later positive component (LPC) over the broad areas that was centered at the midline-central site in both go and stop trials. However, compared to the pattern in go and stop trials with TMS at 500 ms before the target time, N100 and LPC were differently modulated in the go and stop trials with TMS just at the target time. The amplitudes of both N100 and LPC decreased in go trials, while the amplitude of LPC decreased and the latency of LPC was delayed in both go and stop trials. These results suggested that TMS-induced neuronal reactions in the motor cortex and subsequent their propagation to surrounding cortical areas might change functionally according to task demand when executing and inhibiting a motor response.
Highlights
Transcranial magnetic stimulation (TMS; Barker et al, 1985) is a powerful tool that allows for the non-invasive investigation of the functional state of the cerebral cortex and corticomotoneuronal (CM) pathways (Hallett, 2000, 2007; Walsh and Cowey, 2000; Reis et al, 2008)
This combined TMS-EEG technique makes it possible to investigate cortical reactivity and corticocortical connectivity from the spatiotemporal patterns of TMS-evoked potentials (TEP), which consist of peaks of negative/positive oscillations lasting about 300 ms (Komssi and Kähkönen, 2006; Ilmoniemi and Kicic, 2010)
For the mean go response time (RT), 50% STs, and stop-signal reaction time (SSRT) in the no-TMS trials, no significant differences were observed between the contralateral and ipsilateral TMS conditions (Figure 2B). These results indicated that task performances in the go/stop task were not very different between the participants in the contralateral and ipsilateral TMS conditions
Summary
Transcranial magnetic stimulation (TMS; Barker et al, 1985) is a powerful tool that allows for the non-invasive investigation of the functional state of the cerebral cortex and corticomotoneuronal (CM) pathways (Hallett, 2000, 2007; Walsh and Cowey, 2000; Reis et al, 2008). The functional meaning and cortical origin of the TEP peaks are not completely understood, a prominent long-latency negative peak has been commonly observed when TMS is delivered over the motor cortex in many previous studies (Paus et al, 2001; Nikulin et al, 2003; Komssi et al, 2004; Bonato et al, 2006; Kicicet al., 2008; Bonnard et al, 2009; Lioumis et al, 2009; Ferreri et al, 2011, 2012; Rogasch et al, 2013). This reproducible large negative peak at about 100 ms after the TMS pulse is named N1 or N100
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