Department of Psychology, University of California, San Diego 9500 Gilman Drive, La Jolla, CA 92093-0109, USA.
J Neurosci Methods. 2012 Mar 15;204(2):238-41. doi: 10.1016/j.jneumeth.2011.11.020. Epub 2011 Nov 25.
Transcranial magnetic stimulation (TMS) is increasingly used in cognitive neuroscience to probe non-motor cortical regions. A key question for such studies is the choice of stimulation intensity. Early studies used a simple metric such as 115% of motor threshold (MT) for non-motor regions; where MT is the stimulation intensity required to elicit a particular amplitude of motor evoked potential or visible muscle twitch when the coil is placed over primary motor cortex. Recently, however, it was demonstrated that this simple metric for stimulation of non-motor regions is inadequate - it could lead to over or under-stimulation depending on the distance between the coil and the cortex. Instead, a method was developed to scale the motor threshold based on coil-cortex distance, at least for standard figure-of-eight stimulating coils. Here we validate the same method for a 'batwing coil', which is designed to stimulate deeper cortical structures such as the medial frontal cortex. We modulated coil-cortex distance within-participant by inserting spacers of different thickness between coil and scalp. We then measured MT at each spacer. We show that for every millimeter between coil and scalp an additional 1.4% of TMS output is required to induce an equivalent level of brain stimulation at the motor cortex. Using this parameter we describe a linear function to adjust MT for future studies of non-motor regions-of-interest using the batwing coil. This is the first study to demonstrate the effects of coil-cortical distance on stimulation efficiency via a monophasic system using a batwing coil.
经颅磁刺激（TMS）在认知神经科学中越来越多地用于探测非运动皮质区域。对于这类研究，一个关键问题是刺激强度的选择。早期的研究使用了一种简单的指标，如 115%的运动阈值（MT）用于非运动区域；其中 MT 是指在将线圈放置在初级运动皮质上时，产生特定幅度的运动诱发电位或可见肌肉抽搐所需的刺激强度。然而，最近的研究表明，这种用于刺激非运动区域的简单指标是不充分的——它可能导致过度或不足刺激，这取决于线圈和皮质之间的距离。相反，开发了一种基于线圈-皮质距离来调整运动阈值的方法，至少对于标准的 8 字形刺激线圈是如此。在这里，我们验证了相同的方法对于“蝙蝠翼线圈”的有效性，该线圈旨在刺激更深的皮质结构，如内侧前额皮质。我们通过在线圈和头皮之间插入不同厚度的垫片来在参与者内部调节线圈-皮质距离。然后，我们在每个垫片处测量 MT。我们表明，对于线圈和头皮之间的每一毫米距离，需要额外增加 1.4%的 TMS 输出，才能在运动皮质上达到等效的脑刺激水平。使用这个参数，我们描述了一个线性函数，用于调整未来使用蝙蝠翼线圈研究非运动感兴趣区域的 MT。这是第一项通过使用蝙蝠翼线圈的单相系统来证明线圈-皮质距离对刺激效率影响的研究。
