Proefschrift_Holstein

General introduction

Prefrontal control of striatal processing In chapter 7 this idea was tested by assessing whether processing in the prefrontal cortex can alter processing of motivated cognitive control in the striatum ( chapter 1 ). In humans, we can manipulate neural signalling by using non-invasive brain stimulation (transcranial magnetic stimulation; TMS; box 2.5 ). This technique can only target regions near the skull, but previous work has shown that neuronal excitability in regions connected to the stimulated region can also be affected. For example, stimulation of the motor cortex can alter dopamine signalling in the putamen ( figure 2.1: blue ) (Strafella et al., 2003; van Schouwenburg et al., 2012), and this technique thus provides a way by which we can target the striatum after stimulation of a cortical region in human subjects. Using this technique in healthy young human subjects, I aimed to assess the nature of the interactions between the cortex and the striatum. In chapter 7 , I therefore used TMS to temporarily decrease neural signalling in three regions of the cortex ( figure 2.1 ). More specifically, I used this technique to target the cortical regions involved in reward processing, cognitive control (task switching) and action (response switching) ( figure 2.1 ). Combined with fMRI (box 2.4), this enabled me to assess whether stimulation of the cortex could indeed modulate processing in the striatum in a task-specific way. Based on anatomical work ( chapter 1 ), we hypothesized that changing the excitability of the part of the prefrontal cortex involved in reward processing (the anterior prefrontal cortex; figure 2.1: orange ) would affect processing in the part of the striatum implicated in reward processing ( figure 2.1: orange ). In addition, in line with the idea that information transfer between corticostriatal circuits is crucial for adaptive behaviour, we hypothesized that changing processing in the anterior prefrontal cortex could change processing.

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