To what extent electrocorticography (ECoG) and electroencephalography (scalp EEG) differ in their capability to locate sources of deep brain activity is far from evident. Compared to EEG, the spatial resolution and signal-to-noise ratio of ECoG is superior but its spatial coverage is more restricted, as is arguably the volume of tissue activity effectively measured from. Moreover, scalp EEG studies are providing evidence of locating activity from deep sources such as the hippocampus using high-density setups during quiet wakefulness. To address this question, we recorded a multimodal dataset from 4 patients with refractory epilepsy during quiet wakefulness. This data comprises simultaneous scalp, subdural and depth EEG electrode recordings. The latter was located in the hippocampus or insula and provided us with our "ground truth" for source localization of deep activity. We applied independent component analysis (ICA) for the purpose of separating the independent sources in theta, alpha and beta frequency band activity. In all patients subdural- and scalp EEG components were observed which had a significant zero-lag correlation with one or more contacts of the depth electrodes. Subsequent dipole modeling of the correlating components revealed dipole locations that were significantly closer to the depth electrodes compared to the dipole location of non-correlating components. These findings support the idea that components found in both recording modalities originate from neural activity in close proximity to the depth electrodes. Sources localized with subdural electrodes were ∼70% closer to the depth electrode than sources localized with EEG with an absolute improvement of around ∼2cm. In our opinion, this is not a considerable improvement in source localization accuracy given that, for clinical purposes, ECoG electrodes were implanted in close proximity to the depth electrodes. Furthermore, the ECoG grid attenuates the scalp EEG, due to the electrically isolating silastic sheets in which the ECoG electrodes are embedded. Our results on dipole modeling show that the deep source localization accuracy of scalp EEG is comparable to that of ECoG.

中文翻译：

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用头皮和硬膜下脑电图定位大脑深部活动

皮层电图 (ECoG) 和脑电图 (头皮 EEG) 在定位深部大脑活动来源的能力方面有何不同尚不清楚。与 EEG 相比，ECoG 的空间分辨率和信噪比更高，但其空间覆盖范围更受限制，可以说是有效测量的组织活动量。此外，头皮脑电图研究提供了在安静清醒期间使用高密度设置从深源（例如海马体）定位活动的证据。为了解决这个问题，我们记录了 4 名在安静清醒期间患有难治性癫痫的患者的多模式数据集。该数据包括同步头皮、硬膜下和深度 EEG 电极记录。后者位于海马体或脑岛，为我们提供了“基本事实” 用于深度活动的源定位。我们应用独立分量分析 (ICA) 来分离 theta、alpha 和 beta 频带活动中的独立来源。在所有患者中，观察到硬膜下和头皮 EEG 成分与深度电极的一个或多个触点具有显着的零滞后相关性。相关组件的后续偶极子建模揭示了与非相关组件的偶极子位置相比，更靠近深度电极的偶极子位置。这些发现支持这样一种观点，即在两种记录方式中发现的成分都源自靠近深度电极的神经活动。用硬膜下电极定位的源比用 EEG 定位的源更接近深度电极约 70%，绝对改善约 2cm。在我们看来，鉴于出于临床目的，ECoG 电极被植入到靠近深度电极的位置，这在源定位精度方面并没有显着提高。此外，由于嵌入了 ECoG 电极的电绝缘硅橡胶片，ECoG 网格会衰减头皮 EEG。我们对偶极子建模的结果表明，头皮 EEG 的深源定位精度与 ECoG 相当。由于嵌入了 ECoG 电极的电绝缘硅橡胶片，ECoG 网格会衰减头皮 EEG。我们对偶极子建模的结果表明，头皮 EEG 的深源定位精度与 ECoG 相当。由于嵌入了 ECoG 电极的电绝缘硅橡胶片，ECoG 网格会衰减头皮 EEG。我们对偶极子建模的结果表明，头皮 EEG 的深源定位精度与 ECoG 相当。