FIGURE 3.

Illustration of static and dynamic effective connectivity (SEC and DEC) from a neuroimaging standpoint using two experimental fMRI time series. In (A), the two time series seem highly correlated and nearly overlapping. However, the variations in the pink time series do not appear to happen after (or before) the variations in blue time series (top-left figure). This poor causal relationship results in a low SEC value (= 0.07). Correspondingly, DEC values hover around the zero-value (bottom-left figure) since a causal relationship does not seem to emerge for most part of time, except for a brief span (marked by the arrow) when there is a visible causal relationship. In (B), the pink time series seems to constantly follow after the blue time series (top-right figure), indicating that the pink signal’s associated brain region activates (and deactivates) immediately after the blue signal’s region activates (and deactivates), thus a causal relationship and a high SEC value (= 0.95). DEC provides additional insight (bottom-right figure), wherein steady causality is maintained almost for the entire duration except for a brief span (marked by the arrow), wherein DEC dips because of observable lack of causality in the time series’ of those sections.