Hemodynamic Traveling Waves in Human Visual Cortex
Figure 5
Quantifying the spatiotemporal response.
A Calculation of the instantaneous phase reveal phase fronts of the response. These fronts are nearly stationary at the center and propagate with roughly constant velocity away from the center at |x|>1 mm. They are well described with straight line fits, as seen in panel B: toward the fovea (F) (red) and toward the periphery (P) (black). Along these slopes the BOLD signal decays exponentially in time C: with decay constants ΓP = −0.56±0.04 s−1, ΓF = −0.86±0.08 s−1, and D: as a function of perpendicular distance, with decay constants KP = 0.32±0.02 mm−1, KF = 0.38±0.02 mm−1. The error bars are 1 s.e.m, and errors of the parameter estimates are 1 s.d. E: Propagation velocity and damping rate for each of the subjects and their hemispheres. Red data points are the foveal values (F), while values toward the periphery (P) are shown in black. These points show a wide scatter, corresponding to individual differences, but there is a significant positive correlation. A straight line fit to this log-log plot yields an overall trendline that corresponds to a power law with exponent 0.24±0.09 (s.d).