Department of Psychiatry, University of North Carolina, Chapel Hill, NC, USA.
Department of Psychiatry, University of North Carolina, Chapel Hill, NC, USA; Carolina Center for Neurostimulation, University of North Carolina, Chapel Hill, NC, USA; Neuroscience Center, University of North Carolina, Chapel Hill, NC, USA; Department of Cell Biology and Physiology, University of North Carolina, Chapel Hill, NC, USA; Department of Biomedical Engineering, University of North Carolina, Chapel Hill, NC, USA; Department of Neurology, University of North Carolina, Chapel Hill, NC, USA.
Brain Stimul. 2022 Mar-Apr;15(2):472-482. doi: 10.1016/j.brs.2022.02.014. Epub 2022 Feb 25.
Alpha oscillations have been proposed to provide phasic inhibition in the brain. Yet, pinging alpha oscillations with transcranial magnetic stimulation (TMS) to examine phase-dependent network excitability has resulted in conflicting findings. At the cellular level, such gating by the alpha oscillation remains poorly understood.
We examine how the excitability of pyramidal cells and presumed fast-spiking inhibitory interneurons depends on the phase of the alpha oscillation.
Optogenetic stimulation pulses were administered at random phases of the alpha oscillation in the posterior parietal cortex (PPC) of two adult ferrets that expressed channelrhodopsin in pyramidal cells. Post-stimulation firing probability was calculated as a function of the stimulation phase of the alpha oscillation for both verum and sham stimulation.
The excitability of pyramidal cells depended on the alpha phase, in anticorrelation with their intrinsic phase preference; pyramidal cells were more responsive to optogenetic stimulation at the alpha phase with intrinsically low firing rates. In contrast, presumed fast-spiking inhibitory interneurons did not show such a phase dependency despite their stronger intrinsic phase preference.
Alpha oscillations gate input to PPC in a phase-dependent manner such that low intrinsic activity was associated with higher responsiveness to input. This finding supports a model of cortical oscillation, in which internal processing and communication are limited to the depolarized half-cycle, whereas the other half-cycle serves as a signal detector for unexpected input. The functional role of different parts of the alpha cycle may vary across the cortex depending on local neuronal firing properties.
阿尔法振荡被认为在大脑中提供阶段性抑制。然而，用经颅磁刺激（TMS）敲击阿尔法振荡来检查与相位相关的网络兴奋性，得到的结果却相互矛盾。在细胞水平上，这种阿尔法振荡的门控作用仍知之甚少。
我们研究了锥体神经元和假定的快速放电抑制性中间神经元的兴奋性如何依赖于阿尔法振荡的相位。
在两只成年雪貂的后顶叶皮层（PPC）中，随机施加阿尔法振荡的光遗传学刺激脉冲，这两只雪貂的锥体神经元中表达了通道视紫红质。将刺激后的放电概率作为阿尔法振荡的刺激相位的函数进行计算，分别为真刺激和假刺激。
锥体神经元的兴奋性依赖于阿尔法相位，与它们的内在相位偏好呈反相关；在内在放电率较低的阿尔法相位，锥体神经元对光遗传学刺激的反应性更高。相比之下，尽管假定的快速放电抑制性中间神经元具有更强的内在相位偏好，但它们并没有表现出这种相位依赖性。
阿尔法振荡以依赖相位的方式对 PPC 进行输入门控，使得内在活动较低与对输入的更高反应性相关。这一发现支持了一种皮层振荡模型，其中内部处理和通信仅限于去极化的半周期，而另一半周期则作为对意外输入的信号检测器。根据局部神经元放电特性，不同部分的阿尔法周期的功能作用可能会在皮层中有所不同。
