  A recurrent idea in the study of complex systems is that optimal information
processing is to be found near bifurcation points or phase transitions.
However, this heuristic hypothesis has few (if any) concrete realizations where
a standard and biologically relevant quantity is optimized at criticality. Here
we give a clear example of such a phenomenon: a network of excitable elements
has its sensitivity and dynamic range maximized at the critical point of a
non-equilibrium phase transition. Our results are compatible with the essential
role of gap junctions in olfactory glomeruli and retinal ganglionar cell
output. Synchronization and global oscillations also appear in the network
dynamics. We propose that the main functional role of electrical coupling is to
provide an enhancement of dynamic range, therefore allowing the coding of
information spanning several orders of magnitude. The mechanism could provide a
microscopic neural basis for psychophysical laws.
