Effects of Transcranial Stimulation With Direct and Alternating Current on Resting-State Functional Connectivity: An Exploratory Study Simultaneously Combining Stimulation and Multiband Functional Magnetic Resonance Imaging

Abstract

Background: Transcranial stimulation with direct (tDCS) and alternating current (tACS) has increasingly gained interest in various fields, from cognitive neuroscience to clinical investigations. Transcranial current stimulation used alone may modulate brain activity that consequently influences behaviors, without providing information on potentially induced brain activity changes. The combination of transcranial current stimulation and functional magnetic resonance imaging (fMRI) may help to address this. This exploratory study investigated instantaneous and subsequent effects of tDCS and tACS on restingstate functional connectivity (rsFC) in healthy adults. Methods: We conducted a randomized crossover study with 15 healthy subjects receiving three stimulation conditions (tDCS, tACS, and sham) on separate days. Stimulation was applied over the left and right dorsolateral prefrontal cortex (DLPFC) for 30 min (1 mA). rsFC of the targeted prefrontal areas was assessed before, during, and after stimulation using multiband fMRI and using left and right DLPFC as seeds. Results: Both tDCS and tACS increased rsFC during and after the stimulation period, as compared to sham. tDCS-induced changes were observed between the left DLPFC and bilateral parietal regions at the junction of the superior parietal and the inferior parietal lobules. tACS-induced changes were observed between the left DLPFC and the right inferior parietal lobule. Conclusion: Overall, these results suggest that a single session with a low dose, 1 mA, of tDCS or tACS can cause changes in fronto-parietal connectivity that occur rapidly, that is,

Transcranial Direct Current Stimulation Modulates Connectivity of Left Dorsolateral Prefrontal Cortex with Distributed Cortical Networks

“…Whereas Keeser et al (2011) focused on the connectivity strength changes in different brain networks, other research focused on pairwise connectivity between lDLPFC and other brain regions. Using a seed-based connectivity analysis, Mondino et al (2020) showed that the lDLPFC stimulation increased resting-state functional connectivity between lDLPFC and bilateral parietal regions (IPL, SPL). IPL and SPL belong to FPCN, and therefore these findings are consistent with our finding that lDLPFC connectivity within FPCN was increased by stimulation.…”

“…However, the connectivity changes specific to lDLPFC or between lDLPFC and the networks were not directly tested in this study. In another study, connectivity analyses using lDLPFC as the seed region showed that the stimulation increased connectivity between lDLPFC and bilateral parietal regions inferior parietal lobule [IPL], superior parietal lobule [SPL]); however, this study focused on pairwise functional connectivity relationships and did not take the network structure into consideration (Mondino et al, 2020).…”

Effects of Transcranial Alternating Current Stimulation and Neurofeedback on Alpha (EEG) Dynamics: A Review

“…The effects of tACS or NFB on brain plasticity have been already investigated by using fMRI (Kluetsch et al, 2014 ; Nicholson et al, 2016 ; Abellaneda-Pérez et al, 2020 ; Gundlach et al, 2020 ; Mondino et al, 2020 ; Chen et al, 2021 ), the measurement of a motor-evoked potential (MEP) by transcranial magnetic stimulation (TMS) (Ros and Gruzelier, 2011 ; Wach et al, 2013 ; Vallence et al, 2021 ). The link between EEG changes and changes in the levels of the concentration of the molecular substrates of plasticity after tACS/NFB intervention has been already studied too Lee et al, 2019 ; Wischnewski et al, 2019 ; Markiewicz and Dobrowolska, 2020 ; Riddle et al, 2020a ).…”

Alpha Oscillatory Activity Causally Linked to Working Memory Retention: Insights from Online Phase-corrected Closed-loop Transcranial Alternating Current Stimulation (tACS)

“…Anti-phase tACS disturbed frontoparietal alpha synchronization compared to in-phase tACS. Previous studies have reported the potential impact of tACS on functional connectivity (29,30) and found increases in the strength of alpha synchronization with increasing memory load among the frontoparietal regions known to underlie executive and attentional functions during WM maintenance (31,32), so online tACS effects in frontoparietal alpha synchronization were also assessed. The phase lag index (PLI) was used to describe frontoparietal alpha synchronization considering its reliable estimates of phase synchronization against the presence of volume conduction (33).…”