Fig. S4.

Histograms of simulated cell polarizations. Histograms of simulated cellular polarizations including all polarization measurements (gray) and only those that occurred following the first depolarization of a cell (red) for the conditions C₀ = 0, ΔC = 0 (A); C₀ = 0, ΔC = Low (B); C₀ = 0, ΔC = High (C); and C₀ = Medium, ΔC = 0 (D). (E) Directional repolarization statistics for simulated cells as a function of the amount of time between removal and reintroduction of chemokine for two parameters of the time scale of the memory kernel: smaller time scale with τ = 1 in blue and a larger time scale with τ = 1,000 in green. The larger time scale exhibits longer memory compared with the smaller time scale, with a higher fraction of cells repolarizing in the same direction at any time. (F) For slow waves, where the time scale of the positive gradient τ_Δn = 200 is larger than the time scale of the memory kernel τ_pc =100, the polarization of the membrane switches directions as seen by the final negative p(t) at long times. (G) For faster waves, where τ_Δn = 100 is comparable to τ_pc, the cell exhibits directional memory and does not switch polarization directions, as seen by the positive p(t) at long times. Details are found in Results.