School of Electronics Engineering, Kyungpook National University, Daegu, 41566, South Korea; School of Electronic and Electrical Engineering, Kyungpook National University, Daegu, 41566, South Korea; Carolina Center for Neurostimulation, University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599, USA; Department of Psychiatry, University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599, USA.
Carolina Center for Neurostimulation, University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599, USA; Department of Psychiatry, University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599, USA; Department of Neurology, University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599, USA; Department of Biomedical Engineering, University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599, USA; Department of Cell Biology and Physiology, University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599, USA; Neuroscience Center, University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599, USA.
Brain Stimul. 2021 Mar-Apr;14(2):304-315. doi: 10.1016/j.brs.2021.01.018. Epub 2021 Jan 28.
Single-pulse transcranial magnetic stimulation (TMS) elicits an evoked electroencephalography (EEG) potential (TMS-evoked potential, TEP), which is interpreted as direct evidence of cortical reactivity to TMS. Thus, combining TMS with EEG can be used to investigate the mechanism underlying brain network engagement in TMS treatment paradigms. However, controversy remains regarding whether TEP is a genuine marker of TMS-induced cortical reactivity or if it is confounded by responses to peripheral somatosensory and auditory inputs. Resolving this controversy is of great significance for the field and will validate TMS as a tool to probe networks of interest in cognitive and clinical neuroscience.
Here, we delineated the cortical origin of TEP by spatially and temporally localizing successive TEP components, and modulating them with transcranial direct current stimulation (tDCS) to investigate cortical reactivity elicited by single-pulse TMS and its causal relationship with cortical excitability.
We recruited 18 healthy participants in a double-blind, cross-over, sham-controlled design. We collected motor-evoked potentials (MEPs) and TEPs elicited by suprathreshold single-pulse TMS targeting the left primary motor cortex (M1). To causally test cortical and corticospinal excitability, we applied tDCS to the left M1.
We found that the earliest TEP component (P25) was localized to the left M1. The following TEP components (N45 and P60) were largely localized to the primary somatosensory cortex, which may reflect afferent input by hand-muscle twitches. The later TEP components (N100, P180, and N280) were largely localized to the auditory cortex. As hypothesized, tDCS selectively modulated cortical and corticospinal excitability by modulating the pre-stimulus mu-rhythm oscillatory power.
Together, our findings provide causal evidence that the early TEP components reflect cortical reactivity to TMS.
单脉冲经颅磁刺激（TMS）会引发诱发电位（TMS 诱发电位，TEP），这被解释为 TMS 引起皮质反应的直接证据。因此，TMS 与脑电图（EEG）相结合可用于研究 TMS 治疗模式下脑网络参与的机制。然而，关于 TEP 是否是 TMS 诱导皮质反应的真实标志物，或者它是否受到外周感觉和听觉输入反应的干扰，仍存在争议。解决这一争议对该领域具有重要意义，并将验证 TMS 作为探测认知和临床神经科学中感兴趣网络的工具。
通过对连续 TEP 成分进行空间和时间定位，并利用经颅直流电刺激（tDCS）对其进行调制，我们描绘了 TEP 的皮质起源，以研究单脉冲 TMS 引起的皮质反应及其与皮质兴奋性的因果关系。
我们采用双盲、交叉、假对照设计，招募了 18 名健康参与者。我们采集了经左初级运动皮层（M1）超阈值单脉冲 TMS 刺激诱发的运动诱发电位（MEPs）和 TEP。为了对皮质和皮质脊髓兴奋性进行因果测试，我们在左 M1 施加 tDCS。
我们发现最早的 TEP 成分（P25）定位于左 M1。随后的 TEP 成分（N45 和 P60）主要定位于初级体感皮层，这可能反映了手部肌肉抽搐的传入输入。较晚的 TEP 成分（N100、P180 和 N280）主要定位于听觉皮层。正如假设的那样，tDCS 通过调制刺激前的 mu 节律振荡功率选择性地调制皮质和皮质脊髓兴奋性。
总之，我们的研究结果提供了因果证据，表明早期 TEP 成分反映了 TMS 引起的皮质反应。
