  We address a question on the effect of common stochastic inputs on the
correlation of the spikes trains of two neurons when they are possibly
nonidentical and are coupled through direct connections. We show that the
change in the correlation of low amplitude stochastic inputs can be better
detected when the neurons are connected by direct excitatory couplings.
Depending on whether the neurons are identical or they are slightly different,
symmetric or asymmetric connections can increase the sensitivity of the system
to the input correlation by changing the mean slope of correlation transfer
function over a given range of input correlation. In either case, there is also
an optimum value for synaptic strength which maximizes the sensitivity of the
system to the changes in input correlation.
