The accurate measurement of brain activity by Brain-Machine-Interfaces (BMI) and closed-loop Deep Brain Stimulators (DBS) is one of the most important steps in communicating between the brain and subsequent processing blocks. In conventional chest-mounted systems, frequently used in DBS, a significant amount of artifact can be induced in the sensing interface, often as a common-mode signal applied between the case and the sensing electrodes. Attenuating this common-mode signal can be a serious challenge in these systems due to finite common-mode-rejection-ratio (CMRR) capability in the interface. Emerging BMI and DBS devices are being developed which can mount on the skull. Mounting the system on the cranial region can potentially suppress these induced physiological signals by limiting the artifact amplitude. In this study, we model the effect of artifacts by focusing on cardiac activity, using a current- source dipole model in a torso-shaped volume conductor. Performing finite element simulation with the different DBS architectures, we estimate the ECG common mode artifacts for several device architectures. Using this model helps define the overall requirements for the total system CMRR to maintain resolution of brain activity. The results of the simulations estimate that the cardiac artifacts for skull-mounted systems will have a significantly lower effect than non-cranial systems that include the pectoral region. It is expected that with a pectoral mounted device, a minimum of 60-80 dB CMRR is required to suppress the ECG artifact, while in cranially-mounted devices, a 20 dB CMRR is sufficient, in the worst-case scenario. The methods used for estimating cardiac artifacts can be extended to other sources such as motion/muscle sources. The susceptibility of the device to artifacts has significant implications for the practical translation of closed-loop DBS and BMI, including the choice of biomarkers and the design requirements for insulators and lead systems.

中文翻译：

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生理伪像及其对脑机界面设计的启示

通过脑机接口（BMI）和闭环深度脑刺激器（DBS）准确测量大脑活动是在大脑与后续处理模块之间进行交流的最重要步骤之一。在DBS中经常使用的常规胸部安装系统中，通常会在外壳和感应电极之间施加共模信号，因此会在感应界面中引起大量伪像。由于接口中的有限共模抑制比（CMRR）功能，在这些系统中衰减该共模信号可能是一个严峻的挑战。正在开发可以安装在头骨上的新兴BMI和DBS设备。将系统安装在颅骨区域可以通过限制伪影振幅来潜在地抑制这些诱发的生理信号。在这个研究中，我们在躯干形状的体积导体中使用电流源偶极子模型，通过关注心脏活动来模拟伪影的效果。通过使用不同的DBS架构执行有限元仿真，我们估计了几种设备架构的ECG共模伪像。使用此模型有助于定义整个系统CMRR的总体需求，以维持大脑活动的分辨率。仿真结果估计，与包括胸腔区域的非颅骨系统相比，颅骨安装系统的心脏伪影将具有明显较低的影响。预期对于胸式安装的设备，至少需要60-80 dB的CMRR才能抑制ECG伪影，而在颅骨式安装的设备中，在最坏的情况下，20 dB CMRR就足够了。用于估计心脏伪影的方法可以扩展到其他来源，例如运动/肌肉来源。设备对伪影的敏感性对闭环DBS和BMI的实际转换具有重大意义，包括生物标记的选择以及绝缘子和引线系统的设计要求。