Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA, USA.
J Neurophysiol. 2012 Dec;108(12):3233-8. doi: 10.1152/jn.01058.2011. Epub 2012 Sep 19.
It is well known that spiking neurons can produce action potentials in response to extracellular stimulation above certain threshold. It is widely assumed that there is no upper limit to somatic stimulation, except for cellular or electrode damage. Here we demonstrate that there is an upper stimulation threshold, above which no action potential can be elicited, and it is below the threshold of cellular damage. Existence of this upper stimulation threshold was confirmed in retinal ganglion cells (RGCs) at pulse durations ranging from 5 to 500 μs. The ratio of the upper to lower stimulation thresholds varied typically from 1.7 to 7.6, depending on pulse duration. Computational modeling of extracellular RGC stimulation explained the upper limit by sodium current reversal on the depolarized side of the cell membrane. This was further confirmed by experiments in the medium with a low concentration of sodium. The limited width of the stimulation window may have important implications in design of the electro-neural interfaces, including neural prosthetics.
众所周知，锋电位神经元可以在细胞外刺激超过一定阈值时产生动作电位。人们普遍认为，除了细胞或电极损伤之外，体细胞刺激没有上限。在这里，我们证明存在一个上限刺激阈值，超过该阈值就无法引发动作电位，而该阈值低于细胞损伤的阈值。在脉冲持续时间为 5 到 500 微秒的视网膜神经节细胞 (RGC) 中证实了这种上限刺激阈值的存在。根据脉冲持续时间的不同，上限与下限刺激阈值的比值通常在 1.7 到 7.6 之间变化。对细胞外 RGC 刺激的计算模型通过细胞膜去极化侧的钠离子电流反转解释了上限。在钠离子浓度较低的培养基中的实验进一步证实了这一点。刺激窗口的有限宽度可能对电神经接口的设计（包括神经假体）具有重要意义。
