Boolean Networks and their dynamics are of great interest as abstract modeling schemes in various disciplines, ranging from biology to computer science. Whereas parallel update schemes have been studied extensively in past years, the level of understanding of asynchronous updates schemes is still very poor. In this paper we study the propagation of external information given by regulatory input variables into a random Boolean network. We compute both analytically and numerically the time evolution and the asymptotic behavior of this propagation of external regulation (PER). In particular, this allows us to identify variables which are completely determined by this external information. All those variables in the network which are not directly fixed by PER form a core which contains in particular all non-trivial feedback loops. We design a message-passing approach allowing to characterize the statistical properties of these cores in dependence of the Boolean network and the external condition. At the end we establish a link between PER dynamics and the full random asynchronous dynamics of a Boolean network.
PACS numbers:The main motivation for this work is to study the propagation of external information given by regulating but non-regulated variables into random Boolean networks. This process, called propagation of external regulation, eventually stops due to one of two reasons: Either the external information has propagated throughout the full network, or a core of variables cannot be fixed by PER. The statistical properties of these cores are determined by the ratio α between the numbers of Boolean constraints and of variables, and by the composition of the constraints. In this work we will embed the propagation dynamics of the external condition into the asynchronous update dynamics by introducing ternary variables of values {0, 1, ⋆}. The supplementary joker value ⋆ indicates that a variable has not been fixed to a Boolean value in the PER dynamics. The introduction of this new value ⋆ allow us to analyze the PER dynamics in terms of a new constraint satisfaction problem with the same topology of the original one, but where Boolean constraints are extended in a natural way in order to include this ternary representation. This observation allows us to apply recently developed tools from the statistical-mechanics approach to combinatorial optimization problems.