Figure 4.

Burst initiation and velocity of propagation bursts in PDMS topographical cultures

(A) Spatial distribution of burst initiation points (black dots) and probability density functions of burst initiation (pdf, blue-yellow colormap) for the PDMS configurations shown in Figure 2 and comparing two days in vitro, DIV 7 and DIV 14. $\lambda$ is the Gini coefficient and indicates the degree of focalization of burst initiation. White scale bars are 1 mm and apply to all culture types.

(B) Boxplots of the distribution of $\lambda$ values for all experimental repetitions. At DIV 7, the $\lambda$ distribution for controls is significantly higher (gray asterisks) than for tracks/squares. The $\lambda$ distribution for squares at DIV 14 is significantly higher than the one at DIV 7 (black asterisks). ∗p < 0.05, ∗∗p < 0.01, ∗∗∗p < 0.001 (Student’s t-test).

(C) Top, representative network bursts at DIV 14 that encompass the entire network and whose propagation is compatible with a circular or flat front. The white dot marks the origin of activity. Bottom, corresponding determination of velocity propagation as linear fits, where the Euclidean distance of each ROI to the origin of activity is plotted as a function of its activation time. The squares configuration exhibits a sudden, 2-fold increase in velocity. All linear fits have Pearson’s correlation coefficients $r\gtrsim 0.95$.

(D) Boxplots of propagation velocities for the three configurations, showing that fronts in tracks or squares configurations propagate much slowly than on controls. ∗∗∗p < 0.001 (Student’s t-test).

(E) Local velocities in the tracks configuration, illustrating that activity propagation along the tracks (vertical direction) is much higher than across them (horizontal direction). Arrows marks tracks with high propagation speed and therefore very small color variation.

(F) Boxplots of velocity propagation for different fronts of the same culture. On average, propagation along tracks is 18 mm/s, about 6 times larger than across tracks, which is of 3.5 mm/s ∗∗p < 0.01 (Student’s t-test).