Fig. 1
A population of N uncoupled neurons is driven by common processes (green box) and independent noise processes (blue boxes). The common processes consist of a strong common noise 
and a common sensory signal 
, which is multiplied with a small positive scaling parameter 
. Independent noise processes 
are multiplied with another small positive scaling parameter 
. In the special case of 
, 
the sensory signal is absent and the N neurons exhibit spontaneous activity. Due to the strong common noise ξ the spontaneous activity is highly correlated. In the special case of 
, 
all neurons generate identical output spike trains encoding the sensory signal in the time-dependent firing rate. The output of the population is quantified by the sum 
of the individual spike trains