Proefschrift_Holstein

Controlling dorsolateral striatal function via anterior frontal cortex stimulation

men) who completed all sessions. All participants had normal or corrected-to-normal vision, were right-handed and pre-screened for claustrophobia, psychiatric, neurological, and vascular disorders, drug and medication use, alcohol consumption and smoking behavior, as well as any contraindications for TMS and MRI. Participants gave written informed consent according to the guidelines of the local ethics committee on research involving human participants (CMO Arnhem / Nijmegen: 2011/244). They received course credits or payment for their participation. Experimental design and procedures All sessions took place at the Donders Centre for Cognitive Neuroimaging in Nijmegen, The Netherlands. The experiment consisted of four visits to the center: one ‘intake’ session and three experimental sessions. The intake session consisted of three parts: MRI, questionnaires and TMS. During the MRI part, participants were introduced to the paradigm and completed two practice blocks ( paradigm, figure 7.3, box 2.3 ). A third practice block was completed in the scanner during the acquisition of a structural scan ( MRI acquisition ). Finally, we determined the active motor threshold (aMT) and participants were familiarized with the sensation of cTBS in order to ensure tolerability of cTBS over the stimulation sites (TMS procedure). After successful completion of the intake session, three experimental sessions followed. During each experimental session, participants performed the paradigms twice in the fMRI environment (i.e. they completed two runs in each session). These sessions were separated by one week and for each participant the variation in start time between these three sessions was never more than one hour. To account for nonspecific effects related to the day rather than to TMS, the task was administered twice during each session: once after TMS (stimulation), where the mean time between the start of cTBS and the task was 10.31 minutes (SE: 0.18) ( figure 7.2b ) and once without the prior influence of TMS (baseline). Finally, to control for order effects, 14 participants first performed the baseline fMRI run, followed by TMS and another fMRI run (stimulation fMRI; top panel figure 7.2b ), whereas the remaining 13 participants started with TMS and fMRI, followed by a 30 minute break and another fMRI run (baseline fMRI) to allow for the TMS effects to wear off. Previous work has shown that effects of cTBS over the motor cortex on MEP amplitudes last up to 50 minutes after stimulation, but are no longer present after 60 minutes (Huang et al., 2005; Wischnewski and Schutter, 2015). In the current study, approximately 93 minutes ( bottom panel figure 7.2b ) passed between the administration of cTBS and the start of the baseline task. The time between two runs in a session and between TMS and the start of the task did not vary as a function of stimulation site (all F’s < 1.17, all p’s > 0.3).

143