Figure 1. Methodology used to extract functional connectivity patterns from cytosolic Ca²⁺ traces.

A Image of an islet of Langerhans showing the relative intensity of fluorescence signal during sustained activity (HG). Red circles indicate two cells, i and j, which we regard in continuation. B Temporal evolution of global calcium activity characterized by the mean-field of all beta cells in the islet. In the intervals 0≤t≤150 and 754≤t≤1960 cells were exposed to 6 mM glucose, whereas for 150≤t≤754 a stimulating concentration of glucose (12 mM) was applied. Arrows above the temporal trace denote five different dynamical regimes considered in this study: low glucose prior to stimulation (LG1) – 0≤t<300, activation of beta cells (ON) – 300≤t<420, sustained activity in high glucose (HG) – 600≤t<1000, deactivation of beta cells (OFF) – 1080≤t<1200, and the low glucose after stimulation (LG2) – 1400≤t<1800. Note that the calcium activity pattern has been normalized to the unit interval. C Highlighted dynamical responses of cells i and j during the HG regime. D Correlation diagram for fluorescence signals of the i-th and j-th cell. E The correlation matrix for all pair wise determined R_ij. F The corresponding connectivity matrix (thresholded matrix, R _th = 0.75). G Functional connectivity map in the islet for the HG regime. Red circles indicate cells i and j.