Page 88 - Bladder Dysfunction in the Context of the Bladder-Brain Connection - Ilse Groenendijk.pdf

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Chapter 4
Distances
The distances between activation foci of penile shaft and feet representations in S1 and the cerebellum were measured (Table 2). In S1, vertex distances were measured over the cortical surfaces created during the inflation process in Freesurfer. This gives a more true representation of distances between cortical representations due to the high degree of folding of the postcentral gyrus. Since the cerebellum is not included in the inflation process, Euclidean distances were measured between cerebellar activation foci of penile shaft and feet representations. The distance between neighbouring body representa- tions reflects the amount of cortical space taken up by those representations.22 For example, a piano player will have larger digit representations than average, leading to a measurably larger distance between the thumb and the little finger. If, for example through underuse, the penile shaft representation gets smaller, this should have an ef- fect on the distance between penile shaft and foot activation foci.
Table 2. Distances between group penile shaft and foot activation foci in S1 and cerebellum
Table 2. The distances between penile shaft and foot activation foci in both hemispheres at group level. Brain regions in which distances were measured are indicated in brackets. Distances measured in Euclidean space are indicated with an asterisk. S1: primary somatosensory cortex, Cb: cerebellum
DISCUSSION
The present study is the first to investigate genital touch with the extensive field of view as supported by 7T imaging, and by doing so it provides novel data on the precise rep- resentations of the genitalia in the human brain, in particular those of hindbrain areas like the cerebellum that were often omitted with other approaches. By exploiting the increased BOLD sensitivity and specificity available at 7T, we obtained data with high spatial acuity and anatomical specificity. These clearly demonstrate that the genitalia are located in the groin region and not below the feet in S1. Furthermore, considerable differences were observed in whole-brain activation patterns in response to tactile stimulation of the genitalia as opposed to the feet. Tactile stimulation of the penile shaft evoked significant activations of discriminative (sensorimotor) and affective (emotional) brain regions, whereas tactile stimulation of the feet evoked significant activations of
Hemisphere
Distance (mm)
penile shaft - foot (S1)
L
27.5
R
26.8
penile shaft - penile shaft (superomedial- inferolateral S1)
L
64.8
R
63.1
penile shaft - foot (Cb)
L
20.9*
R
28.1*