Kunigk Nicolas G, Urdaneta Morgan E, Malone Ian G, Delgado Francisco, Otto Kevin J
J. Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Gainesville, FL, United States.
Department of Neuroscience, University of Florida, Gainesville, FL, United States.
Front Neurosci. 2022 Jun 17;16:876142. doi: 10.3389/fnins.2022.876142. eCollection 2022.
Intracortical microstimulation (ICMS) has shown promise in restoring quality of life to patients suffering from paralysis, specifically when used in the primary somatosensory cortex (S1). However, these benefits can be hampered by long-term degradation of electrode performance due to the brain's foreign body response. Advances in microfabrication techniques have allowed for the development of neuroprostheses with subcellular electrodes, which are characterized by greater versatility and a less detrimental immune response during chronic use. These probes are hypothesized to enable more selective, higher-resolution stimulation of cortical tissue with long-term implants. However, microstimulation using physiologically relevant charges with these smaller-scale devices can damage electrode sites and reduce the efficacy of the overall device. Studies have shown promise in bypassing this limitation by spreading the stimulation charge between multiple channels in an implanted electrode array, but to our knowledge the usefulness of this strategy in laminar arrays with electrode sites spanning each layer of the cortex remains unexplored. To investigate the efficacy of simultaneous multi-channel ICMS in electrode arrays with stimulation sites spanning cortical depth, we implanted laminar electrode arrays in the primary somatosensory cortex of rats trained in a behavioral avoidance paradigm. By measuring detection thresholds, we were able to quantify improvements in ICMS performance using a simultaneous multi-channel stimulation paradigm. The charge required per site to elicit detection thresholds was halved when stimulating from two adjacent electrode sites, although the overall charge used by the implant was increased. This reduction in threshold charge was more pronounced when stimulating with more than two channels and lessened with greater distance between stimulating channels. Our findings suggest that these improvements are based on the synchronicity and polarity of each stimulus, leading us to conclude that these improvements in stimulation efficiency per electrode are due to charge summation as opposed to a summation of neural responses to stimulation. Additionally, the per-site charge reductions are seen regardless of the cortical depth of each utilized channel. This evocation of physiological detection thresholds with lower stimulation currents per electrode site has implications for the feasibility of stimulation regimes in future advanced neuroprosthetic devices, which could benefit from reducing the charge output per site.
皮层内微刺激（ICMS）已显示出有望改善瘫痪患者的生活质量，特别是当应用于初级体感皮层（S1）时。然而，由于大脑的异物反应导致电极性能的长期退化，这些益处可能会受到阻碍。微制造技术的进步使得具有亚细胞电极的神经假体得以发展，其特点是具有更大的通用性，并且在长期使用过程中免疫反应的危害较小。这些探针被认为能够通过长期植入实现对皮质组织更具选择性、更高分辨率的刺激。然而，使用这些较小规模设备施加生理相关电荷进行微刺激可能会损坏电极部位并降低整个设备的功效。研究表明，通过在植入电极阵列的多个通道之间分散刺激电荷可以绕过这一限制，但据我们所知，这种策略在跨越皮层各层的电极部位的层状阵列中的有效性仍未得到探索。为了研究在具有跨越皮质深度的刺激部位的电极阵列中同时进行多通道ICMS的效果，我们在经过行为回避范式训练的大鼠的初级体感皮层中植入了层状电极阵列。通过测量检测阈值，我们能够使用同时多通道刺激范式来量化ICMS性能的改善情况。当从两个相邻电极部位进行刺激时，每个部位引发检测阈值所需的电荷减半，尽管植入物使用的总电荷量增加了。当使用两个以上通道进行刺激时，阈值电荷的这种降低更为明显，并且随着刺激通道之间距离的增加而减小。我们的研究结果表明，这些改善是基于每个刺激的同步性和极性，这使我们得出结论，每个电极刺激效率的这些提高是由于电荷总和，而不是神经对刺激反应的总和。此外，无论每个使用通道的皮质深度如何，都能看到每个部位电荷的减少。每个电极部位以较低刺激电流诱发生理检测阈值对未来先进神经假体设备中刺激方案的可行性具有重要意义，这些设备可能会从降低每个部位的电荷输出中受益。
