Page 67 - Like me, or else... - Michelle Achterberg

The neural basis of aggression regulation
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Following each peer feedback (positive, neutral, negative), participants were instructed to send a loud noise blast to this peer. The longer they would press a button the more intense the noise would be, which was visually represented by a volume bar (Figure 1b). Participants were specifically instructed that the noise was not really sent to the peer, but that they had to imagine that they could send a noise blast to the peer, with the volume intensity of the participants’ choice. This was done to reduce deception, and prior studies showed that imagined play also leads to aggression (Konijn et al., 2007). Unbeknownst to the participants, the profile was not judged by others, and the photos were taken from an existing data base with pictures matching participants’ age range (Gunther Moor et al., 2010b). Peer pictures were randomly coupled to feedback, ensuring equal gender proportions for each condition. None of the participants expressed doubts about the cover story.
Prior to the scan session, the noise blast was presented to the participants twice during a practice session: once with stepwise buildup of intensity and once at maximum intensity. Two evaluation questions were asked after hearing the maximum intensity: ‘How much do you like the sound?’ and ‘How much do you dislike the sound?’. Participants rated the sound on a 7-point scale, with 1 representing very little and 7 representing very much. In order to prevent that pressing the button during the experimental task would punish the participants themselves, they only heard the intensity of the noise blast during the practice session and not during the fMRI session. To familiarize participants with the task, participants performed six practice trials.
The SNAT consists of two blocks of 30 trials (60 trials in total), with 20 trials for each social feedback condition (positive, neutral, negative), that are presented semi randomized to ensure that no condition is presented more than three times in a row. Figure 1c displays an overview of one SNAT trial. Each trial starts with a fixation screen (500 ms), followed by the social feedback (2500 ms). After another fixation screen (jittered between 3000 and 5000 ms), the noise screen with the volume bar appears, which is presented for a total of 5000 ms. As soon as the participants starts the button press, the volume bar starts to fill up with a newly colored block appearing every 350 ms. After releasing the button, or at maximum intensity (after 3500 ms), the volume bar stops increasing and stays on the screen for the remaining of the 5000 ms. Before the start of the next trial, a fixation cross was presented (jittered between 0 and 11550 ms). The optimal jitter timing and order of events were calculated with Optseq 2 (Dale, 1999).
Exit questions
Following the MRI session, three exit questions were asked: ‘How much did you like reactions with a thumb up?’, ‘How much did you like reactions with a circle?’, and ‘How much did you like reactions with a thumb down?’. Participants rated the
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