The Effect of Transcranial Direct Current Stimulation in Changing Resting-State Functional Connectivity in Patients With Neurological Disorders: A Systematic Review

Abstract

Background: People with neurological disorders are found to have abnormal resting-state functional connectivity (rsFC), which is associated with the persistent functional impairment found in these patients. Recently, transcranial direct current stimulation (tDCS) has been shown to improve rsFC, although the results are inconsistent. Objective: We hope to explore whether tDCS induces rsFC changes among patients with neurological disorders, whether rsFC is clinically relevant and how different tDCS parameters affect rsFC outcome among these individuals. Methods: A systematic review was conducted according to PRISMA guidelines (systematic review registration number: CRD42020168654). Randomized controlled trials that studied the tDCS effects on rsFC between the experimental and sham-controlled groups using either electrophysiological or neuroimaging methods were included. Results: Active tDCS can induce changes in both localized (ie, brain regions under the transcranial electrodes) and diffused (ie, brain regions not directly influenced by the transcranial electrodes) rsFC. Interestingly, fMRI studies showed that the default mode network was enhanced regardless of patients’ diagnoses, the stimulation paradigms used or the rsFC analytical methods employed. Second, stimulation intensity, but not total stimulation time, appeared to positively influence the effect of tDCS on rsFC. Limitations and conclusion: Due to the inherent heterogeneity in rsFC analytical methods and tDCS protocols, meta-analysis was not conducted. We recommend that future studies may investigate the effect of tDCS on rsFC for repeated cathodal stimulation. For clinicians, we suggest anodal stimulation at a higher stimulation intensity within the safety limit may maximize tDCS effects in modulating aberrant functional connectivity of patients with neurological disorders.

Effect of the anodal transcranial direct current electrical stimulation on cognition of medical residents with acute sleep deprivation

“…The acute properties are due to the primary polarization mechanism that induces changes in ionic concentrations (Na+, Ca+, K+, Cl-), alteration of the pH balance, and transmembrane protein variations by synaptic 40 and non-synaptic mechanisms 41 . Active tDCS can induce changes in both local (ie, brain regions under the transcranial electrodes) and diffuse (ie, brain regions remote to the electrodes) regions considering the brain as an anatomic and functional complex neuronal network 42 .…”

Temporal Interference (TI) Stimulation Boosts Functional Connectivity in Human Motor Cortex: A Comparison Study with Transcranial Direct Current Stimulation (tDCS)

“…But in Polania's study, they used electrodes on a 5 × 7 cm area, which covered many brain regions, to deliver current to the scalp. A previous study showed that the size of the electrodes is a factor in modulating the stimulation effect [ 20 ]. In the study of Ho [ 21 ], they found that stimulated with a larger size induced a cumulative enhance in cortical excitability, but not a smaller electrode.…”

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

“…Consistent with previous studies, we found that theta power ( Thibaut et al, 2018 ) and alpha power ( Chennu et al, 2014 ; Cai et al, 2019 ) were significantly and positively correlated with behavioral scores based on the CRS-R. Several studies have confirmed that increased theta, alpha and beta power indicates a better state of consciousness ( Sitt et al, 2014 ; Chennu et al, 2017 ; Huang et al, 2020 ). The effect of tDCS can also appear in other brain regions besides the stimulation site ( Krause et al, 2017 ; Chan and Han, 2020 ). In our study, the stimulation site was in the DLPFC, but the final EEG PSD was significantly different in the parieto-occipital region.…”