Figure 10. Key features of ISMA logic and decision control flow.

During a simulation cycle, each cell steps through five logic modules sequentially to decide which actions to take based on its local environment and internal state. A lumen's target area is adjusted; lumens can merge with each other. Cells that are not dying may begin to do so. Cells adjust their area based on their state and the state of neighboring cells; they stabilize if the lumen has reached a critical size. Cells can create new lumens. Under specified conditions they can divide to form new cells. Future versions of ISMA logic may randomize action control in order to simulate the parallel nature of event occurrence both within MDCK cultures and within each cell. See Figure S12 for complete details of the logic within each of the five modules.