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

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