Departamento de Electromagnetismo y Física de la Materia e Instituto de Física Teórica y Computacional Carlos I Universidad de Granada, Granada, Spain.
PLoS One. 2012;7(8):e40710. doi: 10.1371/journal.pone.0040710. Epub 2012 Aug 7.
Cortical neurons are bistable; as a consequence their local field potentials can fluctuate between quiescent and active states, generating slow 0.5 2 Hz oscillations which are widely known as transitions between Up and Down States. Despite a large number of studies on Up-Down transitions, deciphering its nature, mechanisms and function are still today challenging tasks. In this paper we focus on recent experimental evidence, showing that a class of spontaneous oscillations can emerge within the Up states. In particular, a non-trivial peak around 20 Hz appears in their associated power-spectra, what produces an enhancement of the activity power for higher frequencies (in the 30-90 Hz band). Moreover, this rhythm within Ups seems to be an emergent or collective phenomenon given that individual neurons do not lock to it as they remain mostly unsynchronized. Remarkably, similar oscillations (and the concomitant peak in the spectrum) do not appear in the Down states. Here we shed light on these findings by using different computational models for the dynamics of cortical networks in presence of different levels of physiological complexity. Our conclusion, supported by both theory and simulations, is that the collective phenomenon of "stochastic amplification of fluctuations"--previously described in other contexts such as Ecology and Epidemiology--explains in an elegant and parsimonious manner, beyond model-dependent details, this extra-rhythm emerging only in the Up states but not in the Downs.
皮质神经元是双稳态的；因此，它们的局部场电位可以在静止和活动状态之间波动，产生广泛称为上状态和下状态之间转换的 0.5 2 Hz 缓慢振荡。尽管有大量关于上-下转换的研究，但破译其性质、机制和功能仍然是具有挑战性的任务。在本文中，我们重点介绍了最近的实验证据，表明一类自发振荡可以在上状态中出现。特别是，在其相关的功率谱中出现了一个非平凡的约 20 Hz 的峰值，这导致了更高频率（30-90 Hz 波段）的活动功率增强。此外，由于单个神经元没有锁定在其上，因为它们仍然大部分不同步，因此这种在上状态中的节律似乎是一种涌现或集体现象。值得注意的是，在下降状态中不会出现类似的振荡（以及频谱中的相应峰值）。在这里，我们使用不同的皮质网络动力学计算模型来研究不同生理复杂度水平下的这些发现。我们的结论得到了理论和模拟的支持，即“波动的随机放大”的集体现象——以前在生态学和流行病学等其他背景下有过描述——以一种优雅和简约的方式解释了这种额外的节律仅在上状态中出现而不在下状态中出现的原因，而无需依赖模型的细节。
