identify the 37 consecutive time points of the plateaus (Fig. 2B green and blue curves) corresponding to “word” epochs. This procedure accounted for the initial delay of the hemodynamic response and its return to baseline. The selected time points corresponding to each word epoch were concatenated to form “word” (“Drug” or “Neutral”) time series with 74 time points. “Word” time series were carefully inspected to ensure minimal baseline differences at the concatenation time points, and band-pass filtered (0.01–0.1 Hz; Fig. 2B, red curve), a step that further minimizes this baseline differences. A midbrain region (left substantia nigra, SN; talairach position: xyz = [−6, −15, −18] mm; Fig. 2C, green circle) that showed higher drug-cue related activation for cocaine addicts than for controls using a more complex version of the DW task [15] was selected as the “seed” voxel for the functional connectivity analysis. Whole-brain maps reflecting correlations between BOLD signals in the seed and those in all other voxels in the brain were calculated separately for each “word” time series. The Fisher transform was used to convert the step distributed Pearson linear correlation factors into normally distributed CM coefficients. These normalized CM maps (Fig. 2D) were computed and saved in
