By Dietmar Plenz (Bethesda, MD).

Neurons in cortex synchronize their spiking in response to local and distant inputs. These synchronized assemblies are fundamental to cortex function, yet basic dynamical aspects about their size and duration are largely unknown. Using 2-photon imaging of neurons in superficial cortex of awake mice, we show that synchronized assemblies organize as scale-invariant avalanches that quadratically grow with duration. This quadratic expansion was found for correlated neurons only and required temporal coarse graining, which simulations demonstrated to compensate for spatial subsampling when network dynamics are critical. The corresponding time course of an inverted parabola with collapse exponent of 2 described avalanches of up to 5 s duration and maximized temporal complexity in the ongoing activity of prefrontal and somatosensory cortex and in visual responses of primary visual cortex. Our results identify an extraordinary order in the diverse synchronization of cortical cell assemblies in the form of neuronal avalanches.

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