Department of Physiology and Biomedicine Discovery Institute, Monash University, Clayton, Vic 3800, Australia.
ARC Centre of Excellence for Integrative Brain Function, Clayton, VIC 3800, Australia.
J Neural Eng. 2023 Jun 15;20(3). doi: 10.1088/1741-2552/acdaf7.
Blindness affects approximately 40 million people worldwide and has inspired the development of cortical visual prostheses for restoring sight. Cortical visual prostheses electrically stimulate neurons of the visual cortex to artificially evoke visual percepts. Of the 6 layers of the visual cortex, layer 4 contains neurons that are likely to evoke a visual percept. Intracortical prostheses therefore aim to target layer 4; however, this can be difficult due to cortical curvature, inter-subject cortical variability, blindness-induced anatomical changes in cortex, and electrode placement variations. We investigated the feasibility of using current steering to stimulate specific cortical layers between electrodes in the laminar column.We explored whether the multiunit neural activity peak can be manipulated between two simultaneously stimulating electrodes in different layers of the cortical column. A 64-channel, 4-shank electrode array was implanted into the visual cortex of Sprague-Dawley rats (= 7) orthogonal to the cortical surface. A remote return electrode was positioned over the frontal cortex in the same hemisphere. Charge was supplied to two stimulating electrodes along a single shank. Differing ratios of charge (100:0, 75:25, 50:50) and separation distances (300-500m) were tested.Current steering across the cortical layers did not result in a consistent shift of the neural activity peak. Both single-electrode and dual-electrode stimulation induced activity throughout the cortical column. This contrasts observations that current steering evoked a controllable peak of neural activity between electrodes implanted at similar cortical depths. However, dual-electrode stimulation across the layers did reduce the stimulation threshold at each site compared to single-electrode stimulation.Multi-electrode stimulation is not suitable for targeted activation of layers using current steering. However, it can be used to reduce activation thresholds at adjacent electrodes within a given cortical layer. This may be applied to reduce the stimulation side effects of neural prostheses, such as seizures.
失明影响全球约 4000 万人，这激发了皮质视觉假体的发展，以恢复视力。皮质视觉假体通过电刺激视皮层的神经元来人工诱发视觉感知。在视皮层的 6 层中，第 4 层包含可能诱发视觉感知的神经元。因此，皮质内假体旨在靶向第 4 层；然而，由于皮质曲率、个体间皮质变异性、失明引起的皮质解剖结构变化以及电极放置的变化，这可能很困难。我们研究了使用电流转向在层状柱中的电极之间刺激特定皮质层的可行性。我们探索了是否可以在皮质柱的不同层中的两个同时刺激电极之间操纵多单位神经活动峰值。一个 64 通道、4 臂电极阵列以与皮质表面正交的方式植入 Sprague-Dawley 大鼠（=7）的视皮层。一个远程返回电极放置在同一半球的额皮质上。电荷施加到单个臂上的两个刺激电极上。测试了不同的电荷比（100:0、75:25、50:50）和分离距离（300-500m）。电流转向穿过皮质层并没有导致神经活动峰值的一致移动。单电极和双电极刺激都在整个皮质柱中引起了活动。这与电流转向在植入类似皮质深度的电极之间诱发可控制的神经活动峰值的观察结果形成对比。然而，与单电极刺激相比，跨层的双电极刺激确实降低了每个部位的刺激阈值。多电极刺激不适合使用电流转向进行靶向激活层。然而，它可以用于降低给定皮质层内相邻电极的激活阈值。这可用于减少神经假体的刺激副作用，例如癫痫发作。
