Mia Thomaidou

Chapter 7 – Pharmacological fMRI 223 Materials and Methods Experimental design This randomized clinical trial utilizes a placebo-controlled, double-blind design with respect to the pharmacological administration. A doubleblind randomization list was created by the Leiden University Medical Center (LUMC) pharmacy. Participants were randomly allocated to one of two pharmacological groups: DCS or placebo. All participants underwent nocebo pre-conditioning outside the scanner and acquisition/extinction procedures in the MR scanner, by use of conditioning and negative verbal suggestions. The entire study consisted of two parts in the same testing day. The screening part lasted approximately 1 hour and took place at the department of Social and Behavioral Sciences, Leiden University, the Netherlands. The fMRI part lasted approximately 3 hours, of which approximately 1 hour took place in the 3 Tesla MRI scanner of the Leiden Institute of Brain and Cognition (LIBC) scanning facilities at the LUMC. This study was approved by the Medical Ethics Committee Leiden, The Hague, Delft (P19.003) and pre-registered on ClinicalTrials.gov (NCT04762836). Participants The required sample size for the primary analysis was calculated based on a previous imaging study that, similar to our primary study objective, investigated the effects of DCS in a learning task 32. The analysis was conducted in G*power 3.1 35 for a mixed model analysis of variance (ANOVA). In the experiment by Onur et al. 32 an ANOVA revealed a main effect of the pharmacological agent (DCS vs. placebo) [F(1,27) = 5.454; P = .027] on performance in a declarative learning task. We derived partial η2 from the F statistic and degrees of freedom 36,37. With

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