Many studies have shown that the excitation and inhibition received by cortical neurons remain roughly balanced across many conditions. A key question for understanding the dynamical regime of cortex is the nature of this balancing. Theorists have shown that network dynamics can yield systematic cancellation of most of a neuron’s excitatory input by inhibition. We review a wide range of evidence pointing to this cancellation occurring in a regime in which the balance is loose, meaning that the net input remaining after cancellation of excitation and inhibition is comparable in size with the factors that cancel, rather than tight, meaning that the net input is very small relative to the canceling factors. This choice of regime has important implications for cortical functional responses, as we describe: loose balance, but not tight balance, can yield many nonlinear population behaviors seen in sensory cortical neurons, allow the presence of correlated variability, and yield decrease of that variability with increasing external stimulus drive as observed across multiple cortical areas.

许多研究表明，皮质神经元接收到的兴奋和抑制在许多条件下保持大致平衡。理解皮层动态机制的一个关键问题是这种平衡的本质。理论家已经表明，网络动力学可以通过抑制系统地消除大部分神经元的兴奋性输入。我们审查了广泛的证据，表明这种取消发生在平衡宽松的情况下，这意味着取消兴奋和抑制后剩余的净输入在大小上与取消因素相当，而不是严格的，这意味着净输入相对于抵消因子来说非常小。这种制度的选择对皮质功能反应具有重要意义，正如我们所描述的：松散的平衡，但不是严格的平衡，可以产生在感觉皮层神经元中看到的许多非线性群体行为，允许存在相关的变异性，并且随着时间的推移，这种变异性会降低。在多个皮质区域观察到外部刺激驱动力增加。