The distance between the surface of the scalp and the surface of the grey matter of the brain is a key factor in determining the effective dose of non‐invasive brain stimulation for an individual person. The highly folded nature of the cortical surface means that the depth of a particular brain area is likely to vary between individuals. The question addressed here is: what is the variability of this measure of cortical depth? Ninety‐four anatomical MRI images were taken from the OASIS database. For each image, the minimum distance from each point in the grey matter to the scalp surface was determined. Transforming these estimates into standard space meant that the coefficient of variation could be determined across the sample. The results indicated that depth variability is high across the cortical surface, even when taking sulcal depth into account. This was true even for the primary visual and motor areas, which are often used in setting TMS dosage. The correlation of the depth of these areas and the depth of other brain areas was low. The results suggest that dose setting of TMS based on visual or evoked potentials may offer poor reliability, and that individual brain images should be used when targeting non‐primary brain areas.

中文翻译：

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大脑表面皮层深度的差异：对经颅刺激大脑的影响

头皮表面与大脑灰质表面之间的距离是确定个人无创性脑刺激有效剂量的关键因素。皮质表面高度折叠的性质意味着特定大脑区域的深度可能会因人而异。这里要解决的问题是：这种皮质深度测量的可变性是什么？从OASIS数据库中获取了94幅解剖MRI图像。对于每个图像，确定从灰质中的每个点到头皮表面的最小距离。将这些估计值转换为标准空间意味着可以确定整个样本的变异系数。结果表明，整个皮层表面的深度变化很大，即使考虑到沟深。即使对于通常用于设置TMS剂量的主要视觉和运动区域也是如此。这些区域的深度与其他大脑区域的深度之间的相关性较低。结果表明，基于视觉或诱发电位的TMS剂量设置可能提供较差的可靠性，并且在针对非主要大脑区域时应使用单独的大脑图像。