Abstract
Neuronal avalanches have become an ubiquitous tool to describe the activity of large neuronal assemblies. The emergence of scale-free statistics with well-defined exponents has led to the belief that the brain might operate near a critical point. Yet not much is known in terms of how the different exponents arise or how robust they are. Using calcium imaging recordings of dissociated neuronal cultures we show that the exponents are not universal, and that significantly different exponents arise with different culture preparations, leading to the existence of different universality classes. Naturally developing cultures show avalanche statistics consistent with those of a mean-field branching process, however, cultures grown in the presence of folic acid metabolites appear to be in a distinct universality class with significantly different critical exponents. Given the increased synaptic density and number of feedback loops in folate reared cultures, our results suggest that network topology plays a leading role in shaping the avalanche dynamics. We also show that for both types of cultures pronounced correlations exist in the sizes of neuronal avalanches indicating size clustering, being much stronger in folate reared cultures.
Highlights
The activity of large neuronal assemblies can be described in terms of neuronal avalanches, where groups of consecutive spikes within the whole system are grouped together
Folate reared cultures included 50 nM 5M4Hfolate, a concentration based on maternal serum levels of folic acid resulting from supplementation during pregnancy
Significant deviations from mean–field theory suggest that in contrast to the control case, avalanches in folate reared cultures arise from a much richer dynamics and interactions such that information propagation as captured by neuronal avalanches cannot be well approximated as a simple branching process without feedback loops and/or memory
Summary
The activity of large neuronal assemblies can be described in terms of neuronal avalanches, where groups of consecutive spikes within the whole system are grouped together. MEA have single-cell and sub-millisecond resolution, their typical inter-electrode spacing and overall size makes a large part of the system inaccessible Such spatial undersampling can lead to problems in the analysis of neuronal avalanches[11]. That while the scale-free dynamics of neuronal avalanches persists in the presence of 5M4Hfolate, the critical exponents are significantly different, suggesting a different universality class. This can be interpreted as a significant change in the underlying structural connectivity related to the emergence of pronounced feedback loops[3,17]. We find that the sizes of neuronal avalanches cluster for all different culture preparations such that avalanches tend to be followed by avalanches of similar size; the effect lasting significantly longer in the folate reared cultures
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