  It has recently been reported that statistical signatures of brain
criticality, obtained from distributions of neuronal avalanches, can depend on
the cortical state. We revisit these claims with a completely different and
independent approach, employing a maximum entropy model to test whether
signatures of criticality appear in urethane-anesthetized rats. To account for
the spontaneous variation of cortical state, we parse the time series and
perform the maximum entropy analysis as a function of the variability of the
population spiking activity. To compare data sets with different number of
neurons, we define a normalized distance to criticality that takes into account
the peak and width of the specific heat curve. We found an universal collapse
of the normalized distance to criticality dependence on the cortical state on
an animal by animal basis. This indicates a universal dynamics and a critical
point at an intermediate value of spiking variability.
