2.4 Cocaine and emotional cue reactivity task
During the functional magnetic resonance imaging (fMRI) scan, participants completed a cocaine and emotional cue-reactivity paradigm that consisted of 30 full color cocaine images and 30 emotionally negative images (see Fig. 1). Both conditions were matched with 30 neutral pictures resulting in a total of 120 images. The paradigm consisted of 3 cocaine blocks, 3 emotionally negative blocks, and 6 control blocks. Every block contained 10 pictures that were each presented for 2.5 seconds. The order of the blocks was random (see Fig. 1). A fixation cross was shown for another 2.5 seconds before every block and between the different blocks. All pictures were full-color images and were rescaled to a 448 x 336 pixel dimension. The negative valence pictures were selected from the 65 images of the open affective standardized image set (OASIS)(Kurdi et al. , 2017) that were rated lowest on the valence scale in both sexes. The neutral images were also selected from the OASIS database, particularly those that were rated neutral on the valence scale in both sexes (i.e., between 3.8 and 4.2). Cocaine pictures were derived from an earlier dataset(Kaaget al. , 2018). All neutral images were matched accordingly to the negative images with respect to the scene presented, composition, colors, and sex of the people shown.
Participants were presented with the cue-reactivity paradigm on a screen behind the MRI scanner. They were able to view this screen through a mirror that was placed on the MRI head coil. Participants were asked how they felt to assess affect and how much they craved cocaine before the first block and after every block was presented. These questions were answered through response buttons in which participants had to select a number on a visual analogue scale (VAS) that ranged from 1 (“Sad”/”Not all all”) to 9 (“Happy”/”Extremely”). If no response was given within 5 seconds, the task continued. All fMRI scans were conducted between 3PM and 6PM to minimize potential effects of the time of day on craving.