Preisig Basil C, Hervais-Adelman Alexis
Department of Psychology, Neurolinguistics, University of Zurich, Zurich, Switzerland.
Donders Institute for Cognitive Neuroimaging, Radboud University, Nijmegen, Netherlands.
Front Cell Neurosci. 2022 Feb 22;16:818703. doi: 10.3389/fncel.2022.818703. eCollection 2022.
There is considerable individual variability in the reported effectiveness of non-invasive brain stimulation. This variability has often been ascribed to differences in the neuroanatomy and resulting differences in the induced electric field inside the brain. In this study, we addressed the question whether individual differences in the induced electric field can predict the neurophysiological and behavioral consequences of gamma band tACS. In a within-subject experiment, bi-hemispheric gamma band tACS and sham stimulation was applied in alternating blocks to the participants' superior temporal lobe, while task-evoked auditory brain activity was measured with concurrent functional magnetic resonance imaging (fMRI) and a dichotic listening task. Gamma tACS was applied with different interhemispheric phase lags. In a recent study, we could show that anti-phase tACS (180° interhemispheric phase lag), but not in-phase tACS (0° interhemispheric phase lag), selectively modulates interhemispheric brain connectivity. Using a T1 structural image of each participant's brain, an individual simulation of the induced electric field was computed. From these simulations, we derived two predictor variables: maximal strength (average of the 10,000 voxels with largest electric field values) and precision of the electric field (spatial correlation between the electric field and the task evoked brain activity during sham stimulation). We found considerable variability in the individual strength and precision of the electric fields. Importantly, the strength of the electric field over the right hemisphere predicted individual differences of tACS induced brain connectivity changes. Moreover, we found in both hemispheres a statistical trend for the effect of electric field strength on tACS induced BOLD signal changes. In contrast, the precision of the electric field did not predict any neurophysiological measure. Further, neither strength, nor precision predicted interhemispheric integration. In conclusion, we found evidence for the dose-response relationship between individual differences in electric fields and tACS induced activity and connectivity changes in concurrent fMRI. However, the fact that this relationship was stronger in the right hemisphere suggests that the relationship between the electric field parameters, neurophysiology, and behavior may be more complex for bi-hemispheric tACS.
无创脑刺激的报告有效性存在相当大的个体差异。这种差异通常归因于神经解剖结构的差异以及由此导致的脑内感应电场的差异。在本研究中，我们探讨了感应电场的个体差异是否能够预测γ波段经颅交流电刺激（tACS）的神经生理和行为后果。在一项受试者内实验中，双半球γ波段tACS和假刺激以交替的组块形式施加于参与者的颞上叶，同时通过同步功能磁共振成像（fMRI）和双耳分听任务测量任务诱发的听觉脑活动。γ tACS以不同的半球间相位滞后施加。在最近的一项研究中，我们发现反相tACS（半球间相位滞后180°）而非同相tACS（半球间相位滞后0°）能选择性地调节半球间脑连接。利用每个参与者大脑的T1结构图像，计算了感应电场的个体模拟值。从这些模拟中，我们得出了两个预测变量：最大强度（电场值最大的10000个体素的平均值）和电场精度（假刺激期间电场与任务诱发脑活动之间的空间相关性）。我们发现电场的个体强度和精度存在相当大的差异。重要的是，右半球上方电场的强度预测了tACS诱发的脑连接变化的个体差异。此外，我们在两个半球都发现了电场强度对tACS诱发的血氧水平依赖（BOLD）信号变化影响的统计趋势。相比之下，电场精度并未预测任何神经生理指标。此外，强度和精度均未预测半球间整合。总之，我们发现了电场个体差异与tACS诱发的同步fMRI活动及连接变化之间剂量反应关系的证据。然而，这种关系在右半球更强这一事实表明，双半球tACS的电场参数、神经生理学和行为之间的关系可能更为复杂。
