To clarify this pattern of activation, 2 single-sample t-tests in AFNI compared SWM relative to fixation, and vigilance relative to fixation activations (a < 0.025, ≥943 μl, n = 70). In the SWM relative to fixation contrast, many regions activated preferentially to SWM, and the cingulate/medial frontal gyral region activated more during fixation blocks than during SWM blocks. In the vigilance relative to fixation contrast, the cingulate/medial frontal gyrus cluster, superior cingulate, medial frontal gyrus, and paracentral lobule showed significantly greater BOLD response during fixation blocks, while more inferior areas of the cingulate activated preferentially to the vigilance condition (see Fig. 3). Two separate regressions examined the relationship between BOLD response and FH density for each subregion of activation within the larger cluster, for the vigilance relative to fixation contrast. The superior portion of the cluster, which activated preferentially to the fixation condition, showed a trend-level negative relationship between BOLD response to vigilance relative to fixation and increasing FH density [F(3,62) = 2.49, p = 0.07, β = −0.25, p = 0.07]. The inferior area, which activated preferentially to the
