Frontiers in Systems Neuroscience (Oct 2014)
On the temporal organization of neuronal avalanches
Abstract
Spontaneous activity of cortex in vitro and in vivo has been shown to organize as neuronalavalanches. Avalanches are cascades of neuronal activity that exhibit a power law in theirand duration distribution, typical features of balanced systems in a critical state. Recentlyit has been shown that the distribution of quiet times between consecutive avalanches inrat cortex slice cultures displays a non-monotonic behavior with a power law decay at shorttime scales. This behavior has been attributed to the slow alternation between up and down-states. Here we further characterize the avalanche process and investigate how the functionalbehavior of the quiet time distribution depends on the fine structure of avalanche sequences.By systematically removing smaller avalanches from the experimental time series we showthat size and quiet times are correlated and highlight that avalanche occurrence exhibits thecharacteristic periodicity of θ and β/γ oscillations, which jointly emerge in most of the analyzedsamples. Furthermore our analysis indicates that smaller avalanches tend to be associated withfaster β/γ oscillations, whereas larger ones are associated with slower θ and 1-2 Hz oscillations.In particular, large avalanches corresponding to θ cycles trigger cascades of smaller ones,which occur at β/γ frequency. This temporal structure follows closely the one of nested θ − β/γoscillations. Finally we demonstrate that, because of the multiple time scales characterizingavalanche dynamics, the distributions of quiet times between avalanches larger than a certainsize do not collapse onto a unique function when rescaled by the average occurrence rate.However, when considered separately in the up-state and in the down-state, these distributionsare solely controlled by the respective average rate and two different unique function can beidentified.
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