Before revision:  These FLOW portraits provide an intuitive map of dynamic calcium activity, including sources, sinks, and traveling fronts in the data, using the finite-time Lyapunov exponent (FTLE) technique developed to analyze time-varying manifolds in unsteady fluids.
After revision:  These FLOW portraits provide an intuitive map of dynamic calcium activity, including regions of initiation and termination, as well as the direction and extent of activity spread. To extract these structures, we use the finite-time Lyapunov exponent (FTLE) technique developed to analyze time-varying manifolds in unsteady fluids.