Model outline. The model describes the movement of cells on a longitudinal segment of the plane, discretized into squares (A). On the longitudinal sides, the track has periodic boundary conditions with respect to cell movement and diffusion. At the beginning (t = 0), the cells are placed at the starting point at random positions. At each time point, the cells carry out the algorithm described in the Methods section (Figure 8). As a result, the cells form an advancing front, and at each time T, the distribution of cell density as well as signal concentration is determined. The distributions found are irregular and asymmetrical (inset C).