FIG. 8.

Relationship between signal variation and BOLD signal change and Z-statistic. a: Z-statistic (top) and signal change (bottom) maps for the case example presented in Figure 2. The blue arrow corresponds to a region of higher Z-statistics but lower signal change, whereas the red arrow corresponds to a region of lower Z-statistics but higher signal change. The red arrow is placed in an outer cortical region with venous pooling, whereas the blue arrow is placed medially in a region which likely partial volumes with more microvasculature. b: Signal timecourses for both regions. c,d: Scatter plots for both regions during room air and carbogen administration, respectively. During both conditions, the lower Z-statistic region exhibits significantly higher variance as quantified by a Bartlett test; room air (X² = 22.0; P ≤ 0.025) and carbogen (X² = 20.4; P ≤ 0.025). This is consistent with Z-statistic maps being less sensitive to regions of high signal variation, which may arise nonspecifically in draining veins.