By Woodrow Shew (Fayetteville, AR).

The criticality hypothesis offers an explanation of the observed complexity of brain dynamics and is important because of potential computational advantages near criticality. However, in the awake state, when cortex most needs computation, experimental evidence for criticality has been inconsistent, especially when considering spikes of many single neurons measured with high temporal resolution. The inconsistency of previous reports raises the question: is the awake cortex near criticality or not? Here we show that discrepant previous reports of critical phenomena in the brain may be reconciled by considering dimensionality and dimensionality reduction of brain dynamics. Indeed, fundamental physics of critical phenomena emphasizes the importance of coarse-graining of observables, which is a type of dimensionality reduction. Many detailed microscopic degrees of freedom must be excluded to reveal universal macroscopic features of criticality. We show that coarse graining over neurons and time is a type of dimensionality reduction which reveals low-dimensional critical dynamics in a prominent subspace (first principal component) of cortical dynamics.

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