Hemodynamic Traveling Waves in Human Visual Cortex
Figure 4
Traveling waves on the flattened cortical surface.
A: Normalized Fourier power at the peak response frequency 0.1 Hz, calculated for voxels on the flattened surface, with the red rectangle outlining the response at 0.6° eccentricity (the line of high activation just below is at 1.6°). This power level reveals which voxels respond strongly to the experimental manipulation. B: Voxels that are coherent (Methods) with the stimulus (>0.4) provide an estimate of the approximately straight isoeccentricity curve on the cortex (the solid curve at x = 0). A polynomial curve is fitted to estimate the centerline, and perpendiculars are taken from this to find x. C: Averages of signals at all points with equal x, plotted vs. x and t, showing evidence of damped traveling waves in the form of sloping contours at left and right. The average percentage signal change ranges from −0.4 to 0.4 as indicated by the colorbar. D: Estimate of the 0.1 Hz signal delay from the stimulus onset vs. distance. E: Spatial cross-sections of the spatiotemporal response, relative to baseline, at t = 7.5 s (red), showing a clear rise in amplitude, and at t = 12.5 s (black), the central response has decreased and the surrounding signal remains above baseline.