FIG. 4.

In this second two-group contrast, the SNR levels are the same (in contrast to Fig. 3). The only difference between the two groups is the addition of correlation between regions 1 and 2 (“long range”). The presence of local correlations (within region) is indicated by the color of the square representing each of the three regions (see color bar to the right). The presence of interregional correlations (p<10⁻⁴) is indicated with a colored solid line, whereas dashed lines indicate the absence of correlation. Correlation values here represent group-averaged and connection-averaged values, calculated over all possible seed voxels for each individual simulated subject. The left column shows correlations in group A (row 1) and group B (row 2) prior to GSReg. The second column shows the correlation results after GSReg. Note the distortion of interregional correlations in the two groups, as predicted from the results of Figures 2 and 3. The last column shows the contrast between group correlation maps after GSReg. Note the dramatically different intra- and interregional correlation structure (p<10⁻⁴ for all comparisons), in contrast to the original data, which contained only one real group difference—a long-range positive correlation between regions 1 and 2 in group B.