Fig. 4
a–c In a, the relationship between inverse voxels to CO2 and O2 and age is shown. These data best fit a second-order polynomial; p = 0.029. b Second-level group analysis based on the inverse response to the CO2 ramp (orange voxels). The statistically significant voxels are in the deep periventricular white matter. c Second-level group analysis based on the inverse response to the O2 ramp (orange voxels). The statistically significant voxels are in the prefrontal and medial temporal regions