Signatures of criticality'
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Introduction
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Our perception of the world seems a coherent whole, yet it is built out of the activities of thousands or even millions of neurons, and similarly for our memories, thoughts, and actions. It seems difficult to understand the emergence of behavioral and phenomenal coherence unless the underlying neural activity also is coherent. Put simply, the activity of a brain—or even a small region of a brain devoted to a particular task—cannot be just the summed activity of many independent neurons. But if neurons are not independent, how do we describe their collective activity?

Statistical mechanics provides a language for connecting the interactions among many microscopic degrees of freedom to the macroscopic behavior of matter. Thus, we use statistical mechanics to give a quantitative theory of how a rigid solid emerges from the interactions between atoms, how a magnet emerges from the interactions between electron spins, and so on [@anderson_72; @textbook]. Importantly, these are all collective phenomena: there is no sense in which a single molecule, or even a small cluster, can be described as solid or liquid; rather, solid and liquid are statements about the joint behaviors of many, many molecules.

At the core 