The effects of transcranial direct current stimulation on short-interval intracortical inhibition and intracortical facilitation: a systematic review and meta-analysis

Abstract

<jats:title>Abstract</jats:title> <jats:p>Transcranial direct current stimulation (tDCS) is increasingly being used to affect the neurological conditions with deficient intracortical synaptic activities (i.e. Parkinson’s disease and epilepsy). In addition, it is suggested that the lasting effects of tDCS on corticospinal excitability (CSE) have intracortical origin. This systematic review and meta-analysis aimed to examine whether tDCS has any effect on intracortical circuits. Eleven electronic databases were searched for the studies investigating intracortical changes induced by anodal (a) and cathodal (c) tDCS, in healthy individuals, using two paired-pulse transcranial magnetic stimulation (TMS) paradigms: short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF). Additionally, motor-evoked potential (MEP) size alterations, assessed by single-pulse TMS, were extracted from these studies to investigate the probable intracortical origin of tDCS effects on CSE. The methodological quality of included studies was examined using Physiotherapy Evidence Database (PEDro) and Downs and Black’s (D&amp;B) assessment tools. Thirteen research papers, including 24 experiments, were included in this study scoring good and medium quality in PEDro and D&amp;B scales, respectively. Immediately following anodal tDCS (a-tDCS) applications, we found significant decreases in SICI, but increases in ICF and MEP size. However, ICF and MEP size significantly decreased, and SICI increased immediately following cathodal tDCS (c-tDCS). The results of this systematic review and meta-analysis reveal that a-tDCS changes intracortical activities (SICI and ICF) toward facilitation, whereas c-tDCS alters them toward inhibition. It can also be concluded that increases and decreases in CSE after tDCS application are associated with corresponding changes in intracortical activities. The results suggest that tDCS can be clinically useful to modulate intracortical circuits.</jats:p>

Effects of High-Definition and Conventional Transcranial Direct-Current Stimulation on Motor Learning in Children

“…Mechanisms of tDCS are difficult to study in humans with even more limited knowledge in the developing brain ( Antal et al, 2003 ; Anguera et al, 2007 ; Hummel et al, 2009 ; Lee et al, 2010b ; Biabani et al, 2018 ). Anodal tDCS may modulate neuronal excitability leading to increased spontaneous neuronal firing rates.…”

“…The “callosal access” and “bilateral access” hypothesis proposes that practice-induced motor engrams developed in the dominant hemisphere may be accessed in homologous regions of the opposite motor cortex ( Anguera et al, 2007 ; Lee et al, 2010a ). Others suggest the improvements reflect an increase of excitatory (or decrease of inhibitory) drive toward M1 ( Biabani et al, 2018 ) and paired-pulse TMS studies have demonstrated suppression of intracortical inhibitory systems after tDCS ( Biabani et al, 2018 ). MR spectroscopy studies have also shown a decrease in GABA after M1 tDCS ( Stagg et al, 2014 ).…”

Non-Invasive Cerebellar Stimulation in Neurodegenerative Ataxia: A Literature Review

“…Several factors could have influenced these negative outcomes. Stimulation parameters, such as electrode montage, number of sessions, timing of the onset of stimulation, the selection of tasks that may not entirely depend on cerebellar structures, study design with possible carryover effects between sessions, and sample size, are relevant factors that could explain some of these negative results [88], but further studies are needed clarify these aspects.…”

Evidence for a subcortical contribution to intracortical facilitation

“…The intensity of the conditioning S1 was the same as used in our recent publication (Niemann et al., ), namely 69.4 ± 1.3% of RMT in FCR and 67.5 ± 1.0% of RMT in SOL, which is similar to that applied in previous studies testing ICF (Biabani et al., ).…”