Modelling Cyclic Causal Structures

Many causal systems studied by sciences such as biology, pharmacology, and economics feature causal cycles. Most accounts of causal modelling currently on the market are, however, explicitly designed to study acyclic structures. This chapter focuses on causal cycles and the challenges such cycles pose for causal modelling. First, we distinguish between different types of causal cycles. Then we introduce causal models and discuss a selection of general challenges for cyclic models when it comes to representation, prediction, and causal discovery. Finally, we zoom in on a concrete case from biochemistry: the PI3K/mTOR signalling network that plays a crucial role in regulating the cell cycle. Using this case we discuss some possible pitfalls for the application of causal modelling tools to complex biological cases.