Allison-Walker Tim, Hagan Maureen A, Price Nicholas S C, Wong Yan T
Department of Physiology and Biomedicine Discovery Institute, Monash University, Clayton, Vic, 3800, Australia; ARC Centre of Excellence for Integrative Brain Function, Australia; Monash Vision Group, Monash University, Clayton, Vic, 3800, Australia.
Department of Physiology and Biomedicine Discovery Institute, Monash University, Clayton, Vic, 3800, Australia; ARC Centre of Excellence for Integrative Brain Function, Australia.
Brain Stimul. 2021 Jul-Aug;14(4):741-750. doi: 10.1016/j.brs.2021.04.020. Epub 2021 May 8.
Cortical visual prostheses often use penetrating electrode arrays to deliver microstimulation to the visual cortex. To optimize electrode placement within the cortex, the neural responses to microstimulation at different cortical depths must first be understood.
We investigated how the neural responses evoked by microstimulation in cortex varied with cortical depth, of both stimulation and response.
A 32-channel single shank electrode array was inserted into the primary visual cortex of anaesthetized rats, such that it spanned all cortical layers. Microstimulation with currents up to 14 μA (single biphasic pulse, 200 μs per phase) was applied at depths spanning 1600 μm, while simultaneously recording neural activity on all channels within a response window 2.25-11 ms.
Stimulation elicited elevated neuronal firing rates at all depths of cortex. Compared to deep sites, superficial stimulation sites responded with higher firing rates at a given current and had lower thresholds. The laminar spread of evoked activity across cortical depth depended on stimulation depth, in line with anatomical models.
Stimulation in the superficial layers of visual cortex evokes local neural activity with the lowest thresholds, and stimulation in the deep layers evoked the most activity across the cortical column. In conjunction with perceptual reports, these data suggest that the optimal electrode placement for cortical microstimulation prostheses has electrodes positioned in layers 2/3, and at the top of layer 5.
皮层视觉假体通常使用穿透式电极阵列向视觉皮层传递微刺激。为了优化电极在皮层内的放置，必须首先了解在不同皮层深度对微刺激的神经反应。
我们研究了皮层中微刺激诱发的神经反应如何随刺激和反应的皮层深度而变化。
将一个32通道单杆电极阵列插入麻醉大鼠的初级视觉皮层，使其跨越所有皮层层。在跨越1600μm的深度施加高达14μA的电流进行微刺激（单个双相脉冲，每相200μs），同时在2.25 - 11ms的反应窗口内记录所有通道的神经活动。
在皮层的所有深度，刺激均引起神经元放电率升高。与深部位点相比，浅表刺激位点在给定电流下以更高的放电率做出反应，且阈值更低。诱发活动在皮层深度上的层间传播取决于刺激深度，这与解剖学模型一致。
在视觉皮层浅层进行刺激诱发局部神经活动的阈值最低，而在深层进行刺激诱发跨皮层柱的活动最多。结合感知报告，这些数据表明皮层微刺激假体的最佳电极放置是将电极置于第2/3层以及第5层顶部。
