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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.