EEG modulation by different transcranial direct current stimulation (tDCS) montages: a randomized double-blind sham-control mechanistic pilot trial in healthy participants

Abstract

Background: Based on our Phantom study on transcranial direct current stimulation (tDCS), we hypothesized that EEG band power and field confinement would be greater following left dorsolateral prefrontal cortex (DLPFC -F3) tDCS using circular vs. rectangular electrodes. Methods: Double-blind randomized trial comparing tDCS with anode over the left DLPFC (groups: rectangular electrodes, circular electrodes, sham) and 2 active subgroup references (right shoulder vs. right DLPFC cathodes). Results: Twenty-four randomized participants were assessed. We indeed found higher average EEG power spectral density (PSD) across bands for circular vs. rectangular electrodes, largely confined to F3 and there was a significant increase at AF3 for low alpha (p=0.037). Significant differences included: increased PSD in low beta (p=0.024) and theta bands (p=0.021) at F3, and in theta (p=0.036) at FC5 for the right DLPFC vs. shoulder with no coherence changes. We also found PSD differences between active vs. sham tDCS at Fz for alpha (p=0.043), delta (p=0.036), high delta (p=0.030); and at FC1 for alpha (p=0.031), with coherence differences for F3-Fz in beta (p=0.044), theta (p=0.044), delta (p=0.037) and high delta (p=0.009). Conclusion:This pilot study despite having low statistical power given its small sample size shows that active left DLPFC tDCS modulates EEG frontocentrally and suggests that electrode shapes/reference locations affect its neurophysiological effects, such as increased low alpha power at AF3 using circular vs. rectangular electrodes. Further research with more participants is warranted.

The neuroelectrophysiological and behavioral effects of transcranial direct current stimulation on executive vigilance under a continuous monotonous condition

“…Compared with the sham group, real tDCS significantly increased electrical activity in the left dorsolateral prefrontal and the entire brain cortex, particularly high-frequency electrical activity, i.e., alpha and beta. Similar results were also obtained in previous studies, for example, tDCS to left DLPFC improved alpha power of the prefrontal cortex in patients with a minimally conscious state ( Cavinato et al, 2019 ), and beta PSD of left DLPFC ( El-Hagrassy et al, 2021 ). Although it remains unclear for many oscillatory frequencies whether their activity reflects the engagement or disengagement of sustained attention ( Kamiński et al, 2012 ; Clayton et al, 2015 ), some studies still reflected positive results of oscillatory EEG features and cognitive function.…”

High-Definition Transcranial Direct Current Stimulation of the Dorsolateral Prefrontal Cortex Modulates the Electroencephalography Rhythmic Activity of Parietal Occipital Lobe in Patients With Chronic Disorders of Consciousness

“…The left frontal region included electrodes Fp1, F3, and F7; the right frontal region included electrodes Fp2, F4, and F8; the central region included electrodes Cz, C3, and C4; and the parieto-occipital region included electrodes Pz, P3, P4, O1, and O2. Absolute power spectrum density value (μV 2 /Hz) ( Thatcher et al, 2005 ; El-Hagrassy et al, 2021 ) in each frequency band (delta: 0.1–4 Hz; theta1: 6–8 Hz; theta2: 8–10 Hz; alpha1: 8–10 Hz; alpha2: 10–13 Hz; beta: 13–30 Hz) ( Tarasova et al, 2019 ) were computed using fast Fourier transform with the Welch method ( Welch, 1967 ).…”

Functional Connectivity Increases in Response to High-Definition Transcranial Direct Current Stimulation in Patients with Chronic Disorder of Consciousness

“…There are also many tDCS intervention target options for DOC patients. tDCS can be applied over the left DLPFC, posterior parietal cortex, and left primary sensorimotor cortex [ 6 , 16 , 17 ]. In clinical studies, these above tDCS stimulation targets have been reported to have intervention effects on DOC patients.…”