Figure 2: Optical flow accurately recovers directional propagations in simulated fMRI data.

A) We simulated a wave that travels from the posterior pole to the anterior pole over ≈ 20 seconds. Realistic human BOLD spectral content was enforced in accordance with Laumann et al.⁵⁰. B) To create a reference direction equivalent to ∇FH, we use a scalar map of the posterior-to-anterior (PA) positioning of each point on the cortex. C) We calculated the gradient of this scalar posterior-anterior map (∇PA) over the cortical surface of to serve as a directional reference the cortex to calculate simulated propagation directionality. D) Example directional estimations of optical flow on the simulated wave. White arrows depict activity directionality as estimated by optical flow, and grey vectors depict ∇PA. E) Across cortical areas and timepoints, angular distances between the directions estimated by optical flow aligned with the expected ∇PA reference direction. Inset (top right) depicts the proportion of optical flow vectors within 90 degrees of ∇PA relative to 1,000 null-reference direction distributions (Observed = 0.923, 8.49 S.D. from null directions).