  Feedback in sensory biochemical networks can give rise to bifurcations in
cells' behavioral response. These bifurcations share many properties with
thermodynamic critical points. Evidence suggests that biological systems may
operate near these critical points, but the functional benefit of doing so
remains poorly understood. Here we investigate a simple biochemical model with
nonlinear feedback and multicellular communication to determine if criticality
provides a functional benefit in terms of the ability to gain information about
a stochastic chemical signal. We find that when signal fluctuations are slow,
the mutual information between the signal and the intracellular readout is
maximized at criticality, because the benefit of high signal susceptibility
outweighs the detriment of high readout noise. When cells communicate,
criticality gives rise to long-range correlations in readout molecule number
among cells. Consequently, we find that communication increases the information
between a given cell's readout and the spatial average of the signal across the
population. Finally, we find that both with and without communication, the
sensory benefits of criticality compete with critical slowing down, such that
the information rate, as opposed to the information itself, is minimized at the
critical point. Our results reveal the costs and benefits of feedback-induced
criticality for multicellular sensing.
