Wang Fei, Li Guangli, Chen Jingjing, Duan Yanwen, Zhang Dan
Department of Psychology, School of Social Sciences, Tsinghua University, Beijing 100084, People's Republic of China. Department of Biomedical Engineering, School of Medicine, Tsinghua University, Beijing 100084, People's Republic of China.
J Neural Eng. 2016 Aug;13(4):046021. doi: 10.1088/1741-2560/13/4/046021. Epub 2016 Jul 5.
Modern applications of brain-computer interfaces (BCIs) based on electroencephalography rely heavily on the so-called wet electrodes (e.g. Ag/AgCl electrodes) which require gel application and skin preparation to operate properly. Recently, alternative 'dry' electrodes have been developed to increase ease of use, but they often suffer from higher electrode-skin impedance and signal instability. In the current paper, we have proposed a novel porous ceramic-based 'semi-dry' electrode. The key feature of the semi-dry electrodes is that their tips can slowly and continuously release a tiny amount of electrolyte liquid to the scalp, which provides an ionic conducting path for detecting neural signals.
The performance of the proposed electrode was evaluated by simultaneous recording of the wet and semi-dry electrodes pairs in five classical BCI paradigms: eyes open/closed, the motor imagery BCI, the P300 speller, the N200 speller and the steady-state visually evoked potential-based BCI.
The grand-averaged temporal cross-correlation was 0.95 ± 0.07 across the subjects and the nine recording positions, and these cross-correlations were stable throughout the whole experimental protocol. In the spectral domain, the semi-dry/wet coherence was greater than 0.80 at all frequencies and greater than 0.90 at frequencies above 10 Hz, with the exception of a dip around 50 Hz (i.e. the powerline noise). More importantly, the BCI classification accuracies were also comparable between the two types of electrodes.
Overall, these results indicate that the proposed semi-dry electrode can effectively capture the electrophysiological responses and is a feasible alternative to the conventional dry electrode in BCI applications.
基于脑电图的脑机接口（BCI）的现代应用严重依赖于所谓的湿电极（例如Ag/AgCl电极），这类电极需要涂抹凝胶并对皮肤进行预处理才能正常工作。最近，已开发出替代的“干”电极以提高易用性，但它们常常存在电极与皮肤之间阻抗较高以及信号不稳定的问题。在本文中，我们提出了一种新型的基于多孔陶瓷的“半干”电极。半干电极的关键特性在于其尖端能够缓慢且持续地向头皮释放微量电解液，这为检测神经信号提供了离子传导路径。
通过在五种经典BCI范式中同时记录湿电极对和半干电极对来评估所提出电极的性能：睁眼/闭眼、运动想象BCI、P300拼写器、N200拼写器以及基于稳态视觉诱发电位的BCI。
在所有受试者和九个记录位置上，总体平均时间互相关性为0.95±0.07，并且这些互相关性在整个实验过程中保持稳定。在频谱域中，除了50Hz左右（即电力线噪声）有一个下降外，半干/湿相干性在所有频率下均大于0.80，在10Hz以上频率大于0.90。更重要的是，两种类型电极之间的BCI分类准确率也相当。
总体而言，这些结果表明所提出的半干电极能够有效捕获电生理反应，并且在BCI应用中是传统干电极的一种可行替代方案。
