Division of Electrical, Electronic, and Information Engineering, Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita, Osaka 565-0871, Japan.
J Neural Eng. 2019 Jun;16(3):036007. doi: 10.1088/1741-2552/ab0b80. Epub 2019 Feb 28.
Microstimulation to the cortical tissue applied with penetrating electrodes delivers current that spreads concentrically around the electrode tip and is known to evoke focal visual sensations, i.e. phosphenes. However, to date, there is no direct evidence depicting the spatiotemporal properties of neuronal activity induced immediately after microstimulation and how such activity drives the subsequent local cortical circuits.
In the present study, we imaged the spatiotemporal distribution of action potentials (APs) directly induced by microstimulation and the subsequent trans-synaptic signal propagation using a voltage-sensitive dye (VSD) and a calcium-sensitive dye (CaSD) in slice preparations of the mouse primary visual cortex.
The directly induced APs were confined to the close vicinity of the electrode tip, and the effective distance of excitation was proportional to the square root of the current intensity. The excitation around the electrode tip in layer IV mainly propagated to layer II/III to further induce the subsequent focal activation in downstream local cortical circuits. The extent of activation in the downstream circuits was restrained by competitive interactions between excitatory and inhibitory signals. Namely, the spread of the excitation to lateral neighbor neurons along the layer II/III was confined by the delayed inhibition that also spread laterally at a faster rate.
These observations indicate that dynamic interactions between excitatory and inhibitory signals play a critical role in the focal activation of a cortical circuit in response to intracortical microstimulation and, therefore, in evoking a localized phosphene.
应用穿透电极对皮质组织进行微刺激会产生电流，电流呈同心状扩散，已知会引起焦点视觉感觉，即光幻视。然而，迄今为止，尚无直接证据描述微刺激后立即诱导的神经元活动的时空特性，以及这种活动如何驱动随后的局部皮质回路。
在本研究中，我们使用电压敏感染料 (VSD) 和钙敏感染料 (CaSD) 在小鼠初级视觉皮层的切片中直接成像微刺激直接诱导的动作电位 (AP) 的时空分布和随后的跨突触信号传播。
直接诱导的 AP 局限于电极尖端的附近区域，并且激发的有效距离与电流强度的平方根成正比。电极尖端周围的激发主要传播到第 II/III 层，以进一步在下游局部皮质回路中诱导随后的焦点激活。下游回路中的激活程度受到兴奋性和抑制性信号之间的竞争相互作用的限制。即，兴奋沿着第 II/III 层向侧向相邻神经元的传播受到也以更快速度侧向传播的延迟抑制的限制。
这些观察结果表明，兴奋性和抑制性信号之间的动态相互作用在响应皮质内微刺激对皮质回路的焦点激活中起着关键作用，因此在引发局部光幻视中起着关键作用。
