Predicted current densities in the brain during transcranial electrical stimulation

Abstract

Individually optimized tcMEP monitoring and localized transcranial activation in the brain might be possible through FEM modeling.

Transcranial direct current stimulation (tDCS) in a realistic head model

“…Instead, the geometric mean of reported longitudinal and transverse conductivities was applied to both white matter and muscle tissue. We also compared the results of replacing this geometric mean white matter value with values from the literature, measured either transverse or longitudinal to white matter fibers, to determine the sensitivity of our results to this variation in white matter conductivity (Holdefer et al, 2006). We did not use white matter conductivity values derived from measurements on nonoriented tissue or in nonuniform electric fields (such as in Gabriel et al, 1996).…”

“…Each voxel had dimensions of 1.1 mm × 1.1 mm in the transverse plane and a thickness of 1.4 mm. We defined ten electrically significant tissues within the model-bone, scalp, blood, CSF, muscle, white matter, gray matter, sclera, fat, and cartilage-with conductivity values chosen from reliable reported values obtained from measurements at less than 1 kHz, following Holdefer et al (2006). Sources for conductivities are shown in Table 1.…”

“…Therefore, simulations of current flow have been used to infer these patterns; these simulations have been informative, but studies published to date have a number of recognized limitations. Reported simulations of the distribution of low-frequency electricity in head tissues have been based on either single-slice models of human neuroanatomy (Holdefer et al, 2006) or simplified models of cranial and extracranial components (Datta et al, 2008;Im et al, 2008;Miranda et al, 2006;Wagner et al, 2007a). As a result, inferences drawn from these simulations may be unreliable when applied to actual experimental situations.…”

Implementation of Intraoperative Neurophysiological Monitoring during Endovascular Procedures in the Central Nervous System

“…Both C3/C4 and C1/C2 montages elicit arm and leg MEPs with lower intensity thresholds than C3-C4/Cz and Cz/Cz + 6 cm [15]. Montage at C1/C2 is less potent and activates the corticospinal tract less deeply than at C3/C4, probably because more current shunts through the scalp [13]. Furthermore, it induces less movements disturbing supraselective catheterization during AVM embolizations.…”

“…Short pulse trains of 5-7 square-wave stimuli, with a duration of 0.5 ms, interstimulus intervals of 4 ms, and a constant voltage intensity of up to 300 V, were applied at a repetition rate of 1-2 Hz from C1/C2 or C3/C4, according to the International 10/20 system for EEG electrode placement [7]. The C3/C4 montage is more efficient, partly because less current passes through the scalp between the widely spaced electrodes [13]. However, it can also promote deeper current penetration, which may increase the risk of failing to detect cerebral motor compromise rostral to a deep activation site [14].…”