Page 96 - Bladder Dysfunction in the Context of the Bladder-Brain Connection - Ilse Groenendijk.pdf

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Chapter 4
sponse function (HRF) and temporal derivative as basis functions. Realignment param- eters were added as nuisance regressors to account for confounding motion effects. The response for each task was estimated independently from the others. Activation maps for tactile stimulation of the left and right penile shaft showed a high degree of overlap in both hemispheres, and were therefore conjoined into a single contrast using a global null conjunction analysis47 thresholded at p < 0.05 voxel-based FWE). Activation maps for tactile stimulation of the left and right foot were generated as separate contrasts and thresholded at p < 0.05 FWE.
Second level statistical analysis was conducted using a one-sample t-test on individu- als’ task responses. Likewise, at group level, left and right shaft contrasts were conjoined using a global null conjunction analysis p < 0.005 uncorrected for multiple comparisons. Activation maps for tactile stimulation of the left and right foot were again thresholded at p < 0.005 uncorrected for multiple comparisons. Both single subject and group level cortical activation maps were projected on inflated cortical surfaces created in Free- surfer and sampled halfway the mid-cortical depth in order to avoid vascular artifacts at the pial surface.
Functional connectivity analyses
To further evaluate activation of different networks (i.e. discriminative vs affective), we computed the correlation between timeseries from different ROIs in single subjects. Timeseries were extracted from individual pre-processed contrast images, which were realigned, co-registered and smoothed as described earlier. For the penile shaft, ROIs included were S1, S2, vPMC, posterior and anterior insula, pMCG and the cerebellum. ROIs were isolated using individuals’ contrast images and successfully identified in 9 out of 13 individuals. Activation in the thalamus and mPFC could only be observed in 4 and 5 subjects respectively, and were therefore not included in the functional connectivity analysis. For the feet, included ROIs were the S1, S2, posterior insula and cerebellum. Again, ROIs were isolated using individuals’ contrast images and were successfully iso- lated in 10 out of 13 individuals. Overlapping activation clusters were manually separated in ITK-SNAP (http://www.itksnap.org/). Subsequently, voxel timeseries were extracted from each ROI per single subject and denoised for signal arising from white matter, gray matter and cerebrospinal fluid using linear regression. Connectivity was defined as the linear correlation between timeseries of different ROIs, which was computed with the Pearson’s correlation coefficient. Single subject correlation matrices were used to compute a mean correlation matrix for both the penile shaft and feet.
Data availability
The datasets analyzed during the current study are available in NIFTI format for inter- ested researchers. Please contact the corresponding author to make a request.