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Chapter 7
the six original head motion parameters (3 translation, 3 rotation), their first derivative and
the square of the original and first derivative were included in the model, resulting in 24
motion nuisance regressors (Lund et al., 2005). In addition, we used the mean signal from
the white matter and CSF to account for movement-related intensity changes (Verhagen et
al., 2006). Finally, a high-pass filter (128s) was used to remove low-frequency signals (e.g.
scanner drifts) and an AR(1) model was applied to adjust for serial correlations in the data.
Microtime onsets were adjusted to account for the earlier mentioned slice time correction.
To assess the three main effects and the interaction effects, we generated, for each participant,
a contrast image at the first level for the main effect of Reward (high > low reward cue), and,
time-locked to the target, the main effect of Task switching (task switch > task repeat) and
Response switching (response switch > response repeat). In addition, we generated contrast
images for interactions between these factors (i.e. for the interaction between Reward and
Task switching, between Task switching and Response switching and between Reward, Task
switching and Response switching).
At the second level, the contrast images of each effect were subjected to a full factorial GLM,
taking into account the three TMS sites (aPFC, dlPFC, PMC) and TMS administration
(stimulation or baseline). First, we assessed the main effect of each component of the
paradigm (i.e. Reward, Task switching and Response switching) across all six sessions. We
assessed whether the task elicited a neural response at the stimulation site to assess whether
Table 7.2
Main effect of Task switching
Peak MNI
coordinate
Statistic
x
y
z
t-value
p-value: peak
cluster size
Task switching (switch > repeat)
Frontal lobe
IFG (B9)
S
-40
4
30
6.01
P
FWE
< 0.001
1755
Parietal lobe
Superior parietal lobule (B7)
-24
-66
20
8.72
P
FWE
< 0.001
3760
Temporal lobe
Inferior temporal gyrus
-48
-52
-12
6.84
P
FWE
< 0.001
751
The table shows all areas that were significant at peak P
FWE
< 0.05; IFG: Inferior frontal gyrus; PCC =
posterior cingulate cortex; MD = medial dorsal nucleus; SMA = supplementary motor area; ACC = anterior
cingulate cortex; dlPFC = dorsolateral prefrontal cortex;
BI
= bilateral cluster, B = Brodmann area. s = cluster
falls within the dlPFC stimulation site