Figure 3. An excitable model for signal propagation in biofilms.

(A) Model equation combines excitation (blue) and cell-cell communication (orange) to give rise to excitable propagation. The geometric factor g_j is 1/4 at the cell poles and 1/2 otherwise. (B) A cartoon trace illustrates firing (blue-shading) followed by a refractory period (gray-shading) for a given excitable cell. (C) Cell-cell communication (arrows) allows directional signal propagation from one cell to another. Refractory cells are gray and excited cells are blue. (D) Example model snapshots depict complete signal propagation (direction indicated by arrow, Ɛ = 10 for active cells) in the regime above the percolation threshold (left, ϕ = 0.5) and incomplete signal propagation below the percolation threshold (right, ϕ = 0.2). Both cases have the same values for the dynamic parameters, u_o = 0.01, τ = 300. (E) Example amplitude profiles for the images shown in (D).