Inhibitory neurons and the asymmetric shape of neuronal avalanches

In the last twenty years neuronal avalanches have been deeply investigated, both experimentally and numerically, also framing the results in the context of the avalanche scaling theory. In particular the avalanche shape has recently received a wide attention, also because the existence of a universal shape is an indication of the brain acting at a critical point. Within this scope, the detection of the shape asymmetry and the understanding of the mechanisms leading to it can provide useful insights into brain activity. Experimental data evidence, either symmetric or leftward asymmetry in the shape, results are not confirmed by numerical studies. Here we analyze the role of inhibition, connectivity range, and short term plasticity in determining the avalanche shape in an integrate and fire model. Results indicate that, not only the physiological fraction of inhibitory neurons is crucial to observe leftward asymmetry, but also the different synaptic recovery rates between excitatory and inhibitory neurons, confirming the importance of a dynamic balance between excitation and inhibition in brain activity.