Figure 2. The averaged BOLD signal intensity changes in the left and right visual cortex of the non-headache controls. The five blocks from left to right corresponded to spatial frequencies 0.3, 1.2, 3.0, 6.0, and 9.0 cycles per degree. There was no significant difference of neuronal activity between the left and right visual cortex. 

Figure 4. Spatial frequency dependency of the averaged BOLD signal intensity changes in the left and right visual cortex of the non-headache controls. There was no significant difference of neuronal activity between the left and right visual cortex (Wilcoxon signed-rank test, p>0.075).