Ranck J B
Brain Res. 1975 Nov 21;98(3):417-40. doi: 10.1016/0006-8993(75)90364-9.
(1) There are data on the amount of current necessary to stimulate a myelinated fiber or cell body and/or its axon a given distance away from a monopolar electrode over the entire range of practical interest for intracranial stimulation. Data do not exist for other electrode configurations. (2) Currents from a monopolar cathode of more than 8 times threshold may block action potentials in axons. Therefore, only axons lying in a shell around the electrode are stimulated. Elements very close to the electrode may not be stimulated. Close to an electrode small diameter axons may be stimulated and larger ones may not be. (3) Most, and perhaps all, CNS myelinated fibers have chronaxies of 50-100 musec. When gray matter is stimulated, the chronaxie is often 200-700 musec. It is not clear what is being stimulated in this case. Current-duration relations should be determined for many more responses. (4) There are no current-distance or current-duration data for central finely myelinated or unmyelinated fibers. (5) It takes less cathodal current than anodal to stimulate a myelinated fiber passing by a monopolar electrode. When a monopolar electrode is near a cell body, on the opposite side from the axon, often the lowest threshold is anodal, but sometimes cathodal. Stimulation of a neuron near its cell body is not well understood, but in many cases the axon is probably stimulated. (6) Orientation of cell body and axons with respect to current flow is important. For an axon it is the component of the voltage gradient parallel to the fiber that is important. (7) The pia has a significant resistance and capacitance. Gray matter, white matter, and cerebrospinal fluid have different resistivities, which affect patterns of current flow. (8) More is known about stimulation of mammalian CNS than most workers are aware of. Much of what is unknown seems solvable with current methods.
(1) 对于颅内刺激在实际应用的整个感兴趣范围内，存在关于刺激有髓纤维或细胞体及其轴突在距单极电极一定距离处所需电流大小的数据。对于其他电极配置则不存在相关数据。(2) 来自单极阴极超过阈值8倍以上的电流可能会阻断轴突中的动作电位。因此，只有位于电极周围一层壳内的轴突会被刺激。非常靠近电极的部分可能不会被刺激。靠近电极时，小直径轴突可能被刺激而大直径轴突可能不会。(3) 大多数（或许所有）中枢神经系统有髓纤维的时值为50 - 100微秒。当刺激灰质时，时值通常为200 - 700微秒。在这种情况下不清楚刺激的是什么。对于更多反应，应确定电流 - 持续时间关系。(4) 对于中枢精细有髓或无髓纤维，不存在电流 - 距离或电流 - 持续时间数据。(5) 刺激通过单极电极的有髓纤维时，阴极电流比阳极电流小。当单极电极靠近细胞体且在轴突的另一侧时，通常最低阈值是阳极，但有时是阴极。在细胞体附近刺激神经元的情况还不太清楚，但在许多情况下可能刺激的是轴突。(6) 细胞体和轴突相对于电流方向的取向很重要。对于轴突，重要的是平行于纤维的电压梯度分量。(7) 软脑膜具有显著的电阻和电容。灰质、白质和脑脊液具有不同的电阻率，这会影响电流流动模式。(8) 关于哺乳动物中枢神经系统刺激的了解比大多数研究人员意识到的要多。许多未知的东西似乎用当前方法是可以解决的。
