IEEE Trans Neural Syst Rehabil Eng. 2017 Sep;25(9):1375-1386. doi: 10.1109/TNSRE.2016.2631446. Epub 2016 Nov 22.
Magnetic stimulation is less sensitive to the inflammatory reactions that plague conventional electrode-based cortical implants and therefore may be useful as a next-generation (implanted) cortical prosthetic. The fields arising from micro-coils are quite small however and thus, their ability to modulate cortical activity must first be established. Here, we show that layer V pyramidal neurons (PNs) can be strongly activated by micro-coil stimulation and further, the asymmetric fields arising from such coils do not simultaneously activate horizontally-oriented axon fibers, thus confining activation to a focal region around the coil. The spatially-narrow fields from micro-coils allowed the sensitivity of different regions within a single PN to be compared: while the proximal axon was most sensitive in naïve cells, repetitive stimulation over the apical dendrite led to a change in state of the neuron that reduced thresholds there to below those of the axon. Thus, our results raise the possibility that regardless of the mode of stimulation, penetration depths that target specific portions of the apical dendrite may actually be more effective than those that target Layer 6. Interestingly, the state change had similar properties to state changes described previously at the systems level, suggesting a possible neuronal mechanism underlying such responses.
磁刺激对困扰传统基于电极的皮质植入物的炎症反应不太敏感，因此可能作为下一代（植入式）皮质假体有用。然而，微线圈产生的场非常小，因此必须首先确定其调节皮质活动的能力。在这里，我们表明微线圈刺激可以强烈激活 V 层锥体神经元 (PN)，并且这种线圈产生的不对称场不会同时激活水平方向的轴突纤维，从而将激活限制在围绕线圈的焦点区域。微线圈产生的空间狭窄的场允许比较单个 PN 内不同区域的敏感性：虽然近端轴突在未受刺激的细胞中最敏感，但在树突顶端的重复刺激会导致神经元状态发生变化，从而降低那里的阈值低于轴突的阈值。因此，我们的结果提出了一种可能性，即无论刺激模式如何，针对树突特定部分的穿透深度实际上可能比针对第 6 层的穿透深度更有效。有趣的是，状态变化具有与之前在系统水平上描述的状态变化相似的特性，这表明这种反应可能存在潜在的神经元机制。
