Physics of Psychophysics: Optimal Dynamic Range in a Critical Network

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 phenomenon: a network of excitable elements has its sensitivity
and dynamic range maximized at the critical point of a nonequilibrium
phase transition. This non-linear signal processing is due to creation
and annihilation of excitable waves within the network and is a
generic transduction property of excitable media. Our results are
compatible with recent experimental evidence concerning the essential
role of gap junctions in retinal ganglionar cell output, the large
dynamic range in olfactory glomeruli (where gap junctions have also
been found) and critical avalanches in neural tissue. 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
provides a microscopic neural basis for psychophysical laws, and
suggests a new principle for enhancing sensitivity and dynamic range
in artificial sensors.