Antonio de Candia — Università di Napoli Federico II #
Symmetry breaking and avalanche shapes in modular neural networks #
Experimental evidence suggests that the healthy brain operates near a critical regime, characterized by scale-free neuronal avalanches. Recent research has increasingly focused on the mean temporal profiles of neuronal avalanches, as a more stringent and reliable test for criticality. Scaling arguments predict that, when appropriately rescaled, the mean temporal profiles of avalanches of widely varying durations should collapse onto a single scaling function, often approximated by an inverted parabola. Experimental measurements have revealed clear departures from perfect symmetry, often displaying leftward skewing and extended tails. We have investigated the stochastic Wilson–Cowan model on a modular network, in which synaptic strengths differ between intra-module and inter-module connections. The system exhibits a rich phase diagram, comprising symmetric and "broken symmetry" phases. We found that, at the edge of the transition to a symmetric phase, avalanches are right-ward skewed, as observed also in the non-modular Wilson–Cowan model. On the other hand, at the transition to a "broken symmetry" phase, avalanches become left-ward skewed. We found that in the latter case avalanches proceed in two stages: an initially cooperative regime, where excitatory activity is prevalent, followed by inhibitory competition that selects one dominant module and suppresses the others. This is the relevant mechanism leading to a fast rise of the avalanche, followed by a slower decay, and therefore to leftward asymmetry. These findings contribute to a better understanding of the relationship between brain network topology and functional brain activity.