Proefschrift_Holstein

Chapter 7

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

< 0.001

3760

Superior parietal lobule (B7)

-24

-66

20

8.72

P FWE

Temporal lobe

< 0.001

751

Inferior temporal gyrus

-48

-52

-12

6.84

P FWE

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

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

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