High-Definition Transcranial Direct Current Stimulation Induces Both Acute and Persistent Changes in Broadband Cortical Synchronization: A Simultaneous tDCS–EEG Study

Abstract

The goal of this study was to develop methods for simultaneously acquiring electrophysiological data during high definition transcranial direct current stimulation (tDCS) using high resolution electroencephalography (EEG). Previous studies have pointed to the after effects of tDCS on both motor and cognitive performance, and there appears to be potential for using tDCS in a variety of clinical applications. However, little is known about the real-time effects of tDCS on rhythmic cortical activity in humans due to the technical challenges of simultaneously obtaining electrophysiological data during ongoing stimulation. Furthermore, the mechanisms of action of tDCS in humans are not well understood. We have conducted a simultaneous tDCS-EEG study in a group of healthy human subjects. Significant acute and persistent changes in spontaneous neural activity and event related synchronization (ERS) were observed during and after the application of high definition tDCS over the left sensorimotor cortex. Both anodal and cathodal stimulation resulted in acute global changes in broadband cortical activity which were significantly different than the changes observed in response to sham stimulation. For the group of 8 subjects studied, broadband individual changes in spontaneous activity during stimulation were apparent both locally and globally. In addition, we found that high definition tDCS of the left sensorimotor cortex can induce significant ipsilateral and contralateral changes in event related desynchronization (ERD) and ERS during motor imagination following the end of the stimulation period. Overall, our results demonstrate the feasibility of acquiring high resolution EEG during high definition tDCS and provide evidence that tDCS in humans directly modulates rhythmic cortical synchronization during and after its administration.

Assessing cortical synchronization during transcranial direct current stimulation: A graph-theoretical analysis

“…Nevertheless our results could appear in partial disagreement with some previous studies in which it has been shown that tDCS increased the frequency power (Ardolino et al, 2005;Zaehle et al, 2011;Notturno et al, 2014;Roy et al, 2014). It is important to bear in mind that slight differences in the reported frequency changes could be due to different cortical sites and protocols of stimulation, and among all on the ongoing cerebral activity during recording.…”

“…Because these two local measures are related to the shortest paths related to the examined node, possibly there are no reasons because such measures should change when the network is not required to increase its performance to solve a task. These results have some points in common with previous online tDCS-EEG studies (Mangia et al, 2014;Roy et al, 2014), as well as with offline tDCS-EEG studies (Polania et al, 2011a(Polania et al, , 2011bPellicciari et al, 2013).…”

“…We also did not observe a diffused pattern of local synchronization changes, as we could expect if we were measuring common source activity. We could speculate that such differences may be due to tDCS artefacts, but at the moment component analysis is still an effective approach to reduce such artefacts even if not totally effective (Noury et al, 2016;Roy et al, 2014). Moreover, the spatial distribution of the cathodal induced synchronization changes could hardly be attributed to a stimulation-related artefact.…”

Simultaneous high-definition transcranial direct current stimulation of the motor cortex and motor imagery

“…The change in baseline resting data from pre-stimulation to post-stimulation supports previous work that found increased MEP and global network power post-stimulation [8], [10]. The largest effect was not found directly after stimulation, but at 30 minutes delayed from the end of a 20 minute stimulation session.…”

“…With recently developed high-definition tDCS (HDtDCS) [9] systems, online recording of the EEG during stimulation is possible [10]. This setup also allows a more localized stimulation area, reducing current flow to a limited area within the brain.…”