Department of Clinical Neurophysiology, Georg-August University of Göttingen, Göttingen, Germany.
Neuroimage. 2011 Mar 15;55(2):590-6. doi: 10.1016/j.neuroimage.2010.11.085. Epub 2011 Jan 4.
Measurements of motor evoked potentials (MEPs) have shown that anodal and cathodal transcranial direct current stimulations (tDCS) have facilitatory or inhibitory effects on corticospinal excitability in the stimulated area of the primary motor cortex (M1). Here, we investigated the online effects of short periods of anodal and cathodal tDCS on human brain activity of healthy subjects and associated hemodynamics by concurrent blood-oxygenation-level-dependent (BOLD) functional magnetic resonance imaging (fMRI) at 3T. Using a block design, 20s periods of tDCS at 1 mA intensity over the left M1 altered with 20s periods without tDCS. In different fMRI runs, the effect of anodal or cathodal tDCS was assessed at rest or during finger tapping. A control experiment was also performed, in which the electrodes were placed over the left and right occipito-temporo-parietal junction. Neither anodal nor cathodal tDCS over the M1 for 20s stimulation duration induced a detectable BOLD signal change. However, in comparison to a voluntary finger tapping task without stimulation, anodal tDCS during finger tapping resulted in a decrease in the BOLD response in the supplementary motor area (SMA). Cathodal stimulation did not result in significant change in BOLD response in the SMA, however, a tendency toward decreased activity could be seen. In the control experiment neither cathodal nor anodal stimulation resulted in a significant change of BOLD signal during finger tapping in any brain area including SMA, PM, and M1. These findings demonstrate that the well-known polarity-dependent shifts in corticospinal excitability that have previously been demonstrated using measurements of MEPs after M1 stimulation are not paralleled by analogous changes in regional BOLD signal. This difference implies that the BOLD signal and measurements of MEPs probe diverse physiological mechanisms. The MEP amplitude reflects changes in transsynaptic excitability of large pyramidal neurons while the BOLD signal is a measure of net synaptic activity of all cortical neurons.
运动诱发电位（MEPs）的测量表明，阳极和阴极经颅直流电刺激（tDCS）对初级运动皮层（M1）刺激区域的皮质脊髓兴奋性具有促进或抑制作用。在这里，我们通过在 3T 时进行同时的血氧水平依赖（BOLD）功能磁共振成像（fMRI），研究了阳极和阴极 tDCS 对健康受试者大脑活动的在线影响以及相关的血液动力学。使用块设计，在左侧 M1 上进行 1 mA 强度的 20 秒 tDCS 与没有 tDCS 的 20 秒交替。在不同的 fMRI 运行中，在休息或手指敲击时评估阳极或阴极 tDCS 的效果。还进行了一项对照实验，其中电极放置在左侧和右侧枕颞顶交界处。阳极或阴极 tDCS 对 M1 的 20 秒刺激持续时间不会引起可检测的 BOLD 信号变化。然而，与没有刺激的自愿手指敲击任务相比，阳极 tDCS 在手指敲击时导致补充运动区（SMA）的 BOLD 反应减少。阴极刺激不会导致 SMA 中的 BOLD 反应发生显着变化，但是可以看到活动减少的趋势。在对照实验中，在包括 SMA、PM 和 M1 在内的任何脑区，手指敲击时阴极或阳极刺激均不会导致 BOLD 信号发生显着变化。这些发现表明，以前通过测量 M1 刺激后的 MEPs 显示出的与皮质脊髓兴奋性有关的众所周知的极性依赖性变化，与区域 BOLD 信号的类似变化并不平行。这种差异意味着 BOLD 信号和 MEPs 的测量探测到不同的生理机制。MEP 幅度反映了大锥体神经元的突触间兴奋性变化，而 BOLD 信号是所有皮质神经元净突触活动的度量。
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