Can a time varying external drive give rise to apparent criticality in neural systems?

The finding of power law scaling in neural recordings lendssupport to the hypothesis of critical brain dynamics. However, power laws are not unique to critical systems and can arise from alternative mechanisms. Here, we investigate whether a common time -varying external drive to a set of Poisson units can give rise to neuronal avalanches and exhibit apparent criticality. To o this end,we analytically derive the avalanche size and nd d u ra tion distributions, tri bution s, as well as additionalmeasures, first for homogeneous Poisson activity, and then for slowly varying inhomogeneous poisson activity. We show that homogeneous Poisson activity can -n not give rise to p wer law distributions. Inhomogeneous activity can also not generate Per fect power laws, but it can exhibit approximate Powerlawswithcutoffs that are comparable tothosetypicalIyobserved.nexperimehte.Themechanism of generating apparent criticality t y bytimevay.ngexternalfields,toroes or input may generelizetomanyothersystemslike dynamics of swarms, diseases or extin tion cascades. Here, we illustrate the analytically derived effects for spikerecordingsin vivo and discussapproaches to distinguish true from apparentcriticality'. Ultimately, this requires causal intervention,whiohellow separating internalsyetemproperties from e ternallyimposed ones