Variance in cortical depth across the brain surface: Implications for transcranial stimulation of the brain

Abstract

Non-invasive technologies that read or that stimulate the brain, such as EEG, TMS, or tDCS, frequently make assumptions about the anatomical structure of the brain. This is necessary as, for most participants, the structure of the brain is not visible. Two common examples of this sort of assumption would be the use of a standard brain model in computing the source of dipole components in EEG analysis (e.g., Marin, Guerin, Baillet, Garnero, & Meunier, 1998), or the projection of a tDCS-derived computed electric field onto a standard brain model (e.g., Bikson, Rahman, & Datta, 2012). However, to what extent can we rely on a standard brain image in understanding effects in an individual person? Are there particular regions of the brain where a standardized analysis is inadvisable? The use of transcranial magnetic stimulation (TMS) is a good example of a technology that depends strongly on understanding the structure of the brain. In TMS, a brief electric current through a coil of wire induces a rapidly varying

Transcranial direct current stimulation and sporting performance: A systematic review and meta‐analysis of transcranial direct current stimulation effects on physical endurance, muscular strength and visuomotor skills

“…The challenge of examining the studies and variable results also highlights the need for researchers to map out a clear justification for the selected; parameters stimulation intensity and duration, stimulation montage and participant characteristics such as gender and genetics. The neurophysiological mechanisms of brain stimulation also need to be better understood to reduce the variation caused by the existing methodology (see—Datta et al, 2018 and Davis, 2020).…”

Mapping of Motor Function with Neuronavigated Transcranial Magnetic Stimulation: A Review on Clinical Application in Brain Tumors and Methods for Ensuring Feasible Accuracy

“…Furthermore, the coil-to-cortex distance varies with stimulated cortical regions, which may require adjustment of the applied SI [ 130 , 131 , 135 , 136 , 142 , 143 , 144 ]. Because of the differences between target sites, the SI needs to be adjusted by taking into account the differences in coil-to-cortex distances, the secondary field caused by charge accumulation at conductivity discontinuities, and the coil orientation, and adjustment based only on the SI or primary EF is not sufficient [ 135 ].…”

Effects of transcranial magnetic stimulation on the human brain recorded with intracranial electrocorticography: First-in-human study

“…To evaluate these possibilities, we delivered TMS to a gel phantom with intracranial electrodes placed within the gel and on the surface to mimic human experimental conditions, as used previously to investigate safety related to experiments with intracranial electrodes (Oya et al, 2017). The distance from the TMS coil to the electrode contacts was set to 10 mm, which conservatively approximates the smallest distance possible (and thus the highest amplitude in magnetic field) between the coil and iEEG electrodes in human experiments, where TMS must cross the skin, skull, and cerebrospinal fluid space prior to reaching the electrodes (Davis, 2021; Lu and Ueno, 2017).…”

“…The distance from the TMS coil to the electrode contacts was set to 10 mm, which conservatively approximates the smallest distance possible (and thus the highest amplitude in magnetic field) between the coil and iEEG electrodes in human experiments, where TMS must cross the skin, skull, and cerebrospinal fluid space prior to reaching the electrodes (Davis, 2021;Lu and Ueno, 2017).…”