Fig 1. Sketch describing the concept of memory within a reaction network.

A network is divided into bulk and subnetwork, x axis represents time. Concentration changes in the subnetwork act as signals that leave the subnetwork and travel into the bulk. There they interact with other bulk species and return at a later timepoint via bulk-to-subnetwork interactions. The net effect of such interactions is thus that the subnetwork reacts to its own past. The precise influence of past subnetwork states is governed by memory functions that depend on the time difference, i.e. on how long ago the relevant signal has left the subnetwork.