Murphy Brendan K, Miller Kenneth D
Graduate Group in Biophysics, University of California, San Francisco, San Francisco, CA 94122, USA.
Neuron. 2009 Feb 26;61(4):635-48. doi: 10.1016/j.neuron.2009.02.005.
In cerebral cortex, ongoing activity absent a stimulus can resemble stimulus-driven activity in size and structure. In particular, spontaneous activity in cat primary visual cortex (V1) has structure significantly correlated with evoked responses to oriented stimuli. This suggests that, from unstructured input, cortical circuits selectively amplify specific activity patterns. Current understanding of selective amplification involves elongation of a neural assembly's lifetime by mutual excitation among its neurons. We introduce a new mechanism for selective amplification without elongation of lifetime: "balanced amplification." Strong balanced amplification arises when feedback inhibition stabilizes strong recurrent excitation, a pattern likely to be typical of cortex. Thus, balanced amplification should ubiquitously contribute to cortical activity. Balanced amplification depends on the fact that individual neurons project only excitatory or only inhibitory synapses. This leads to a hidden feedforward connectivity between activity patterns. We show in a detailed biophysical model that this can explain the cat V1 observations.
在大脑皮层中，没有刺激时的持续活动在规模和结构上可能类似于由刺激驱动的活动。特别是，猫初级视觉皮层（V1）中的自发活动具有与对定向刺激的诱发反应显著相关的结构。这表明，从无结构的输入中，皮层回路选择性地放大特定的活动模式。目前对选择性放大的理解涉及通过神经元之间的相互兴奋来延长神经集合的寿命。我们引入了一种不延长寿命的选择性放大新机制：“平衡放大”。当反馈抑制稳定强的递归兴奋时，就会出现强平衡放大，这种模式可能是皮层的典型模式。因此，平衡放大应该普遍地对皮层活动做出贡献。平衡放大取决于单个神经元仅投射兴奋性或仅投射抑制性突触这一事实。这导致了活动模式之间隐藏的前馈连接。我们在一个详细的生物物理模型中表明，这可以解释猫V1的观测结果。
