Irregular spiking of pyramidal neurons organizes as scale-invariant neuronal avalanches in the awake state.
Irregular spiking of pyramidal neurons organizes as scale-invariant neuronal avalanches in the awake state.
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DOI：
10.7554/elife.07224
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发表时间：
2015-07-07
期刊：
影响因子：
7.7
通讯作者：
Plenz D
中科院分区：
文献类型：
--
作者：
Bellay T;Klaus A;Seshadri S;Plenz D
神经元活动的自发波动出现在许多空间和时间尺度的皮层。人口的措施发现，这些波动组织规模不变的神经元雪崩，这表明皮质动力学是至关重要的。然而，宏观动力学依赖于生理状态，并且关于它们的细胞组成、时空起源以及来自突触输入或动作电位（AP）输出的贡献是模糊的。在这里，我们研究自发放电的锥体神经元（PNs）从大鼠皮层浅层在体内和体外使用双光子成像。当动物从麻醉状态过渡到清醒状态时，自发的单个神经元放电不规则地增加，并在组水平上组装成尺度不变的雪崩。在体外尖峰雪崩自然出现，但需要平衡的兴奋和抑制。这表明，神经元雪崩与全球生理状态的觉醒和皮质静息活动组织雪崩从发射的本地PN组的全球人口活动。DOI：http://dx.doi.org/10.7554/eLife.07224.001即使我们没有从事任何特定的任务，大脑也会显示出自发活动的协调模式，这些模式可以通过放置在头皮上的电极进行监测。这种休息活动塑造了大脑对后续刺激的反应方式。静息活动模式的变化见于各种神经和精神疾病，以及睡眠剥夺后的健康个体。大脑的外层被称为皮层。在大范围内，当监测成千上万的神经元时，皮层中的静息活动表明大脑中的传播是有组织的。具体而言，静息活动被发现组织为所谓的神经元雪崩，其中神经元活动的大爆发与中等大小和较小的爆发以非常特征的顺序分组。事实上，这些爆发的大小，也就是说，被解雇的神经元的数量，被发现是规模不变的，也就是说，大爆发的比例，中等规模的爆发是相同的，中等规模的小爆发。这种尺度不变性表明，神经元的爆发并不是相互独立的。然而，很大程度上还不清楚神经元雪崩是如何从单个神经元中产生的，这些神经元只是以嘈杂、不规则的方式放电。Bellay，Klaus等人通过研究大鼠从麻醉中恢复时大脑皮层中一种特殊类型的神经元（称为锥体细胞）的放电模式，对这一过程提供了深入的见解。当动物醒来时，皮层中单个锥体细胞的放电变得比麻醉状态下更不规则。然而，通过研究一组神经元的活动，Bellay、Klaus等人意识到，正是这种更不规则的放电引起了神经元雪崩，而且这种情况只在动物清醒时发生。对实验室中生长的单个锥体细胞的进一步实验证实，神经元雪崩是由单个神经元的不规则放电自发产生的。这些雪崩取决于细胞之间两种类型的活动之间的平衡：导致其他神经元放电的“兴奋性”活动和阻止神经元放电的“抑制性”活动。鉴于休息活动会影响大脑对外界的反应，神经元雪崩的起源可能会为大脑处理信息的方式提供线索。未来的实验还应该研究神经元雪崩的出现标志着大脑从无意识到清醒的转变的可能性。DOI：http://dx.doi.org/10.7554/eLife.07224.002网站
Spontaneous fluctuations in neuronal activity emerge at many spatial and temporal scales in cortex. Population measures found these fluctuations to organize as scale-invariant neuronal avalanches, suggesting cortical dynamics to be critical. Macroscopic dynamics, though, depend on physiological states and are ambiguous as to their cellular composition, spatiotemporal origin, and contributions from synaptic input or action potential (AP) output. Here, we study spontaneous firing in pyramidal neurons (PNs) from rat superficial cortical layers in vivo and in vitro using 2-photon imaging. As the animal transitions from the anesthetized to awake state, spontaneous single neuron firing increases in irregularity and assembles into scale-invariant avalanches at the group level. In vitro spike avalanches emerged naturally yet required balanced excitation and inhibition. This demonstrates that neuronal avalanches are linked to the global physiological state of wakefulness and that cortical resting activity organizes as avalanches from firing of local PN groups to global population activity. DOI: http://dx.doi.org/10.7554/eLife.07224.001 Even when we are not engaged in any specific task, the brain shows coordinated patterns of spontaneous activity that can be monitored using electrodes placed on the scalp. This resting activity shapes the way that the brain responds to subsequent stimuli. Changes in resting activity patterns are seen in various neurological and psychiatric disorders, as well as in healthy individuals following sleep deprivation. The brain's outer layer is known as the cortex. On a large scale, when monitoring many thousands of neurons, resting activity in the cortex demonstrates propagation in the brain in an organized manner. Specifically, resting activity was found to organize as so-called neuronal avalanches, in which large bursts of neuronal activity are grouped with medium-sized and smaller bursts in a very characteristic order. In fact, the sizes of these bursts—that is, the number of neurons that fire—are found to be scale-invariant, that is, the ratio of large bursts to medium-sized bursts is the same as that of medium-sized to small bursts. Such scale-invariance suggests that neuronal bursts are not independent of one another. However, it is largely unclear how neuronal avalanches arise from individual neurons, which fire simply in a noisy, irregular manner. Bellay, Klaus et al. have now provided insights into this process by examining patterns of firing of a particular type of neuron—known as a pyramidal cell—in the cortex of rats as they recover from anesthesia. As the animals awaken, the firing of individual pyramidal cells in the cortex becomes even more irregular than under anesthesia. However, by considering the activity of a group of these neurons, Bellay, Klaus et al. realized that it is this more irregular firing that gives rise to neuronal avalanches, and that this occurs only when the animals are awake. Further experiments on individual pyramidal cells grown in the laboratory confirmed that neuronal avalanches emerge spontaneously from the irregular firing of individual neurons. These avalanches depend on there being a balance between two types of activity among the cells: ‘excitatory’ activity that causes other neurons to fire, and ‘inhibitory’ activity that prevents neuronal firing. Given that resting activity influences the brain's responses to the outside world, the origins of neuronal avalanches are likely to provide clues about the way the brain processes information. Future experiments should also examine the possibility that the emergence of neuronal avalanches marks the transition from unconsciousness to wakefulness within the brain. DOI: http://dx.doi.org/10.7554/eLife.07224.002