Department of Electrical Engineering and Automation, Aalto University, Espoo, Finland. Aalto NeuroImaging, Aalto University, FI00076 AALTO, Espoo, Finland. Author to whom any correspondence should be addressed.
Phys Med Biol. 2019 Mar 14;64(6):065019. doi: 10.1088/1361-6560/ab03f5.
The brain moves when the orientation of the head changes. This inter-postural motion has been shown to affect the distribution of cerebrospinal fluid (CSF). As CSF layer thickness affects the distribution of electric fields (EF) in non-invasive brain stimulation methods such as transcranial direct current (TDCS) and magnetic (TMS) stimulation, possible differences in body position between sessions could affect the stimulation efficacy. Additionally, inter-postural differences might distort the modeling results of TDCS and TMS, as the models are usually built based on magnetic resonance images (MRI) obtained while the subject is in the supine position, whereas the actual stimulation is given while the subject is in an upright position. Here, we studied the effects of changing the position of the subject between supine, prone, and left lateral on the conformation of the brain. This study aimed to determine whether small inter-postural changes in the shape of the brain can affect TDCS and TMS EFs as hypothesized. We obtained MRI from five subjects in each position and used them to build anatomically realistic models for use in finite element simulations of the EFs. Position was found to affect EFs, with them being approximately 10% stronger and more diffuse while subjects were in the prone and left lateral than in the supine positions for TDCS. In TMS, a similar trend was observed, but the effect was smaller, approximately 2%, than that observed for TDCS. Thus, the effect of posture should be considered in the design of TDCS and TMS experiments.
当头部的方向改变时，大脑会移动。这种姿势间的运动已被证明会影响脑脊液（CSF）的分布。由于 CSF 层厚度会影响经颅直流电刺激（TDCS）和磁刺激（TMS）等非侵入性脑刺激方法中电场（EF）的分布，因此治疗期间可能存在的体位差异会影响刺激效果。此外，姿势间的差异可能会扭曲 TDCS 和 TMS 的建模结果，因为这些模型通常是基于受试者处于仰卧位时获得的磁共振成像（MRI）构建的，而实际刺激是在受试者处于直立位置时进行的。在这里，我们研究了在仰卧位、俯卧位和左侧卧位之间改变受试者位置对大脑形态的影响。这项研究旨在确定假设的大脑形状的小姿势间变化是否会影响 TDCS 和 TMS 的 EF。我们在每个位置从 5 个受试者中获得 MRI，并将其用于构建用于 EF 有限元模拟的解剖学真实模型。结果发现，与仰卧位相比，受试者处于俯卧位和左侧卧位时，TDCS 的 EF 大约增强 10%，并且更加扩散；而在 TMS 中，观察到类似的趋势，但影响较小，大约为 2%，比 TDCS 观察到的影响小。因此，在设计 TDCS 和 TMS 实验时应考虑姿势的影响。
