Effects of Electrode Drift in Transcranial Direct Current Stimulation

Abstract

Background Conventional transcranial direct current stimulation (tDCS) methods involve application of weak electrical current through electrodes encased in saline soaked sponges affixed to the head using elastic straps. In the absence of careful preparation, electrodes can drift from their original location over the course of a tDCS session. Objective The current paper investigates the influence of electrode drift on distribution of electric fields generated by conventional tDCS. Methods MRI-derived finite element models of electric fields produced by tDCS were used to investigate the influence of incremental drift in electrodes for two of the most common electrode montages used in the literature: M1/SO (motor to contralateral supraorbital) and F3/F4 (bilateral frontal). Based on these models, we extracted predicted current intensity from 20 representative structures in the brain. Results Results from separate RM-ANOVAs for M1/SO and F3/F4 montages demonstrated that 5% incremental drift in electrode position significantly changed the distribution of current delivered by tDCS to the human brain (F’s > 8.6, p’s<.001). Pairwise comparisons demonstrated that as little as 5% drift was able to produce significant differences in current intensity in structures distributed across the brain (p’s< .03). Conclusions Drift in electrode position during a session of tDCS produces significant alteration in the intensity of stimulation delivered to the brain. Elimination of this source of variability will facilitate replication and interpretation of tDCS findings. Furthermore, measurement and statistically accounting for drift may prove important for better characterizing the effects of tDCS on the human brain and behavior.

The Role of the Frontal and Parietal Cortex in Proactive and Reactive Inhibitory Control: A Transcranial Direct Current Stimulation Study

“…Nevertheless, tDCS is a relatively crude method with low spatial specificity. There exist some computational models that can simulate the current flow in the brain (Brunoni et al, 2015;Woods, Bryant, Sacchetti, Gervits, & Hamilton, 2015;Kuo et al, 2013;CaparelliDaquer et al, 2012;Dmochowski, Datta, Bikson, Su, & Parra, 2011), but they need to be verified with experimental methods. In addition, a combination of tDCS and functional imaging can help to better elucidate the neural mechanisms underlying the stimulation effect.…”

A technical guide to tDCS, and related non-invasive brain stimulation tools

“…Studies monitoring physiological changes following tDCS and computational modeling studies of predicted current flow demonstrate that the relative location of electrodes results in significant differences in where and how much current is delivered to the brain (Minhas et al 2012; Kessler et al 2013b; Woods et al 2015). For example, Nitsche and Paulus (2000) demonstrated that relative differences in electrode locations altered whether or not tDCS impacted TMS generated motor-evoked potentials (MEPs).…”

“…For example, Nitsche and Paulus (2000) demonstrated that relative differences in electrode locations altered whether or not tDCS impacted TMS generated motor-evoked potentials (MEPs). Numerous modeling studies have demonstrated significant differences between relative locations of electrodes, with results varying from stimulation of the whole brain to more selective stimulation of particular lobes of the brain (Minhas et al 2012; Kessler et al 2013b; Woods et al 2015). Woods et al (2015) further demonstrated that as little as 1cm of movement in electrode position significantly altered the distribution of predicted current flow in the brain, as well as the intensity of stimulation in specific brain regions Computational modeling (discussed in detail in a later section) can be a useful tool for the a priori design of tDCS electrode positions for a given study.…”

“…Non-conductive headgear used to position the electrodes on the body or scalp (e.g., elastic straps) are not included in the electrode assembly but are critical for appropriate electrode placement (Woods et al 2015). For tDCS using sponge-covered electrodes, elastic straps are the most commonly used headgear for electrode placement.…”

Application of transcranial direct current stimulation to psychiatric disorders: trends and perspectives

“…Moreover, even a slight (about 5 %) drift of electrodes during stimulation can cause significant change in electric field. (Woods et al 2014) Therefore, current flows may vary substantially, which may cause inconsistent effects between individuals (Horvath et al 2014). The variations of current flow may also be associated with paradoxical stimulation effects, as represented by "cathodal stimulation" and suppressing performance by either anodal or cathodal stimulation (Filmer et al 2013).…”