循环网络中均值驱动和波动驱动的持续活动。
Mean-driven and fluctuation-driven persistent activity in recurrent networks.
作者信息
Renart Alfonso, Moreno-Bote Rubén, Wang Xiao-Jing, Parga Néstor
机构信息
Departamento de Físca Teórica, Universidad Autónoma de Madrid, Cantoblanco 28049, Madrid, Spain.
出版信息
Neural Comput. 2007 Jan;19(1):1-46. doi: 10.1162/neco.2007.19.1.1.
Spike trains from cortical neurons show a high degree of irregularity, with coefficients of variation (CV) of their interspike interval (ISI) distribution close to or higher than one. It has been suggested that this irregularity might be a reflection of a particular dynamical state of the local cortical circuit in which excitation and inhibition balance each other. In this "balanced" state, the mean current to the neurons is below threshold, and firing is driven by current fluctuations, resulting in irregular Poisson-like spike trains. Recent data show that the degree of irregularity in neuronal spike trains recorded during the delay period of working memory experiments is the same for both low-activity states of a few Hz and for elevated, persistent activity states of a few tens of Hz. Since the difference between these persistent activity states cannot be due to external factors coming from sensory inputs, this suggests that the underlying network dynamics might support coexisting balanced states at different firing rates. We use mean field techniques to study the possible existence of multiple balanced steady states in recurrent networks of current-based leaky integrate-and-fire (LIF) neurons. To assess the degree of balance of a steady state, we extend existing mean-field theories so that not only the firing rate, but also the coefficient of variation of the interspike interval distribution of the neurons, are determined self-consistently. Depending on the connectivity parameters of the network, we find bistable solutions of different types. If the local recurrent connectivity is mainly excitatory, the two stable steady states differ mainly in the mean current to the neurons. In this case, the mean drive in the elevated persistent activity state is suprathreshold and typically characterized by low spiking irregularity. If the local recurrent excitatory and inhibitory drives are both large and nearly balanced, or even dominated by inhibition, two stable states coexist, both with subthreshold current drive. In this case, the spiking variability in both the resting state and the mnemonic persistent state is large, but the balance condition implies parameter fine-tuning. Since the degree of required fine-tuning increases with network size and, on the other hand, the size of the fluctuations in the afferent current to the cells increases for small networks, overall we find that fluctuation-driven persistent activity in the very simplified type of models we analyze is not a robust phenomenon. Possible implications of considering more realistic models are discussed.
来自皮层神经元的脉冲序列表现出高度的不规则性,其峰峰间隔(ISI)分布的变异系数(CV)接近或高于1。有人提出,这种不规则性可能反映了局部皮层回路的一种特定动态状态,即兴奋和抑制相互平衡。在这种“平衡”状态下,神经元的平均电流低于阈值,放电由电流波动驱动,从而产生类似泊松分布的不规则脉冲序列。最近的数据表明,在工作记忆实验的延迟期记录的神经元脉冲序列的不规则程度,对于几赫兹的低活动状态和几十赫兹的增强的持续活动状态来说是相同的。由于这些持续活动状态之间的差异不可能归因于来自感觉输入的外部因素,这表明潜在的网络动力学可能支持不同放电率下共存的平衡状态。我们使用平均场技术来研究基于电流的漏电积分发放(LIF)神经元的循环网络中多个平衡稳态的可能存在性。为了评估稳态的平衡程度,我们扩展了现有的平均场理论,以便不仅自洽地确定放电率,而且还确定神经元峰峰间隔分布的变异系数。根据网络的连接参数,我们发现了不同类型的双稳态解。如果局部循环连接主要是兴奋性的,那么两个稳定稳态主要在神经元的平均电流上有所不同。在这种情况下,增强的持续活动状态下的平均驱动是超阈值的,并且通常具有低放电不规则性的特征。如果局部循环兴奋性和抑制性驱动都很大且几乎平衡,甚至由抑制主导,那么两个稳定状态共存,两者都具有亚阈值电流驱动。在这种情况下,静息状态和记忆持续状态下的放电变异性都很大,但平衡条件意味着参数微调。由于所需微调的程度随着网络规模的增加而增加,另一方面,对于小网络,细胞传入电流的波动大小会增加,总体而言,我们发现在我们分析的非常简化的模型类型中,波动驱动的持续活动不是一种稳健的现象。我们讨论了考虑更现实模型的可能影响。