Sohn Won Joon, Lim Jeffrey, Wang Po T, Pu Haoran, Malekzadeh-Arasteh Omid, Shaw Susan J, Armacost Michelle, Gong Hui, Kellis Spencer, Andersen Richard A, Liu Charles Y, Heydari Payam, Nenadic Zoran, Do An H
Department of Neurology, University of California, Irvine, Irvine, CA, United States.
Department of Biomedical Engineering, University of California, Irvine, Irvine, CA, United States.
Front Neurosci. 2023 Jan 12;16:1075971. doi: 10.3389/fnins.2022.1075971. eCollection 2022.
Bi-directional brain-computer interfaces (BD-BCI) to restore movement and sensation must achieve concurrent operation of recording and decoding of motor commands from the brain and stimulating the brain with somatosensory feedback.
A custom programmable direct cortical stimulator (DCS) capable of eliciting artificial sensorimotor response was integrated into an embedded BCI system to form a safe, independent, wireless, and battery powered testbed to explore BD-BCI concepts at a low cost. The BD-BCI stimulator output was tested in phantom brain tissue by assessing its ability to deliver electrical stimulation equivalent to an FDA-approved commercial electrical cortical stimulator. Subsequently, the stimulator was tested in an epilepsy patient with subcortical electrocorticographic (ECoG) implants covering the sensorimotor cortex to assess its ability to elicit equivalent responses as the FDA-approved counterpart. Additional safety features (impedance monitoring, artifact mitigation, and passive and active charge balancing mechanisms) were also implemeneted and tested in phantom brain tissue. Finally, concurrent operation with interleaved stimulation and BCI decoding was tested in a phantom brain as a proof-of-concept operation of BD-BCI system.
The benchtop prototype BD-BCI stimulator's basic output features (current amplitude, pulse frequency, pulse width, train duration) were validated by demonstrating the output-equivalency to an FDA-approved commercial cortical electrical stimulator ( > 0.99). Charge-neutral stimulation was demonstrated with pulse-width modulation-based correction algorithm preventing steady state voltage deviation. Artifact mitigation achieved a 64.5% peak voltage reduction. Highly accurate impedance monitoring was achieved with > 0.99 between measured and actual impedance, which in-turn enabled accurate charge density monitoring. An online BCI decoding accuracy of 93.2% between instructional cues and decoded states was achieved while delivering interleaved stimulation. The brain stimulation mapping ECoG grids in an epilepsy patient showed that the two stimulators elicit equivalent responses.
This study demonstrates clinical validation of a fully-programmable electrical stimulator, integrated into an embedded BCI system. This low-cost BD-BCI system is safe and readily applicable as a testbed for BD-BCI research. In particular, it provides an all-inclusive hardware platform that approximates the limitations in a near-future implantable BD-BCI. This successful benchtop/human validation of the programmable electrical stimulator in a BD-BCI system is a critical milestone toward fully-implantable BD-BCI systems.
用于恢复运动和感觉的双向脑机接口（BD-BCI）必须实现大脑运动指令的记录和解码以及利用体感反馈刺激大脑的并发操作。
将能够引发人工感觉运动反应的定制可编程直接皮层刺激器（DCS）集成到嵌入式BCI系统中，以形成一个安全、独立、无线且由电池供电的测试平台，以低成本探索BD-BCI概念。通过评估其提供与FDA批准的商用皮层电刺激器等效电刺激的能力，在虚拟脑组织中测试了BD-BCI刺激器的输出。随后，在一名患有覆盖感觉运动皮层的皮层下脑电描记术（ECoG）植入物的癫痫患者中测试了该刺激器，以评估其引发与FDA批准的同类产品等效反应的能力。还在虚拟脑组织中实施并测试了其他安全功能（阻抗监测、伪迹减轻以及被动和主动电荷平衡机制）。最后，在虚拟大脑中测试了交错刺激与BCI解码的并发操作，作为BD-BCI系统的概念验证操作。
通过证明与FDA批准的商用皮层电刺激器的输出等效性（>0.99），验证了台式BD-BCI刺激器原型的基本输出特征（电流幅度、脉冲频率、脉冲宽度、串持续时间）。基于脉宽调制的校正算法实现了电荷中性刺激，防止了稳态电压偏差。伪迹减轻使峰值电压降低了64.5%。测量阻抗与实际阻抗之间的相关性>0.99，实现了高精度的阻抗监测，进而能够进行准确的电荷密度监测。在进行交错刺激时，指令线索与解码状态之间的在线BCI解码准确率达到了93.2%。癫痫患者大脑刺激映射的ECoG网格显示，两种刺激器引发的反应等效。
本研究展示了集成到嵌入式BCI系统中的全可编程电刺激器的临床验证。这种低成本的BD-BCI系统安全且易于用作BD-BCI研究的测试平台。特别是，它提供了一个全面的硬件平台，近似于未来可植入BD-BCI的限制。在BD-BCI系统中对可编程电刺激器进行的成功台式/人体验证是迈向完全可植入BD-BCI系统的关键里程碑。
