Comparison of Cephalic and Extracephalic Montages for Transcranial Direct Current Stimulation—A Numerical Study

Abstract

While studies have shown that the application of transcranial direct current stimulation (tDCS) has been beneficial in the stimulation of cortical activity and treatment of neurological disorders in humans, open questions remain regarding the placement of electrodes for optimal targeting of currents for a given functional area. Given the difficulty of obtaining in vivo measurements of current density, modeling of conventional and alternative electrode montages via the finite element method has been utilized to provide insight into tDCS montage performance. It has been shown that extracephalic montages might create larger total current densities in deeper brain regions, specifically in white matter as compared to an equivalent cephalic montage. Extracephalic montages might also create larger average vertical current densities in the primary motor cortex and in the somatosensory cortex.At the same time, the horizontal current density either remains approximately the same or decreases. The metrics used in this paper include either the total local current density through the entire brain volume or the average vertical current density as well as the average horizontal current density for every individual lobe/cortex.

Sensorimotor Rhythm BCI with Simultaneous High Definition-Transcranial Direct Current Stimulation Alters Task Performance

“…The variability across study design and parameters within MI and BCI performance, and across tDCS studies, in general, suggest significant avenues for future investigation to optimize stimulation for the target task. Recent computer modeling work has suggested that use of simulation pipelines may help improve optimal stimulation [54–56]. Overall, the behavioral and electrophysiological results combined suggest that anodal tDCS is differentially affecting right and left hand motor imagination.…”

Tempering Proactive Cognitive Control by Transcranial Direct Current Stimulation of the Right (but Not the Left) Lateral Prefrontal Cortex

“…The electrode of interest was placed, depending on the group, over the left DLPFC (F3), the right DLPFC (F4), or the right IFJ (FC6h: midway between FC4 and FC6; see Figure 3). The reference electrode was always placed extracephalically (contralateral shoulder) to minimize its effect on the brain (Noetscher et al, 2014). Stimulation lasted 20 min with a constant current of 2 mA (current density = 0.057 mA/cm 2 ) and was faded in and out with an 8 s ramp.…”

Understanding the behavioural consequences of noninvasive brain stimulation

“…The fact that potential behavioural effects induced by the 'return' electrode are rarely measured does not alleviate the conceptual problem inherent in the idea of selectively influencing the function of a single brain region. This problem may be alleviated by the use of inert (e.g., extracephalic) return electrodes [38,39], asymmetrical electrode sizes [40], or more complex multi-electrode, high-definition (HD) tDCS montages [41].…”