Until recently it was not possible to reliably perform single subject dynamic brain imaging of central urogenital tract control due to the limited resolution of the PET and MRI scanners (1, 2). The introduction of high field 7T MRI scanners offers the possibility to obtain significant results in single subjects due to the increased signal-to-noise ratio (SNR) and blood-oxygenation-level-dependent (BOLD) sensitivity.
The aim of this study was to acquire single subject neural representations of male genital touch and pelvic floor motor control in the whole-brain, and to analyse the results at both single-subject and group level.

17 healthy male subjects (age 20-47, range) were scanned in a 7T MRI scanner (Philips Achieva), of which 4 subjects were excluded due to motion. All subjects completed the same scanning protocol, consisting of 4 functional runs (2 sensory tasks; 2 motor tasks) using a multiband echo planar imaging sequence (voxel size 1.77 x 1.77 x 1.75 mm3; matrix size 104 x 127; FOV 184x223 mm2; number of slices = 70; TR/TE = 2000/25 ms), followed by a T1-weighted anatomical scan (voxel size 0.7 x 0.7 x 0.7 mm3; matrix size 352 x 353, FOV = 246 mm; TR/TE = 4.4/1.97 s). All functional runs were performed using a block paradigm. Sensory tasks included subjects undergoing bilateral tactile stimulation of the penile shaft, and as control tactile stimulation of the medial aspect of the feet. Motor tasks included subjects performing repetitive pelvic floor contractions, and as a control horizontal tongue movements. Activation maps were generated using the General Linear Model (GLM) in SPM12. Single subject activation maps were thresholded at p < 0.05 FWE and projected on inflated cortical surfaces of individual anatomical data. Group activation maps were thresholded at p < 0.005 uncorrected and projected on an inflated cortical surface of the MNI-template. 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 analysis p < 0.005 uncorrected.

Activation was seen during sensory tasks in the primary and secondary sensory cortex (S1 and S2), anterior and posterior insula, posterior cingulate gyrus and the anterior lobe of the cerebellum (n=13). During the motor tasks, active clusters were found in the primary motor cortex (M1), supplementary motor area, anterior insula, putamen, thalamus and the anterior lobe of the cerebellum. Figure 1 (sensory) and figure 2 (motor) show the cortical activation clusters on the inflated MNI brain of the group (n=13) and 6 single subjects. Our connectivity analyses showed a correlation between cerebellar activations and cortical activation for both sensory as motor tasks.

The single-subject  and group analyses showed that S1 activation during sensory stimuli of the penile shaft is located more dorsolateral than activation during tactile stimulation of the feet which is in agreement with previous literature (3). Cortical activation during straining of the pelvic floor is located at the medial aspect of the precentral gyrus M1, while tongue movement resulted in activation of the lateral aspect of both M1 and S1. There were some inconsistencies between single subject and group analysis, for instance frontal lobe activation during the sensory task found in the group analysis but not consistently in all single subjects. Therefore, both single subject and group analyses might provide a complementary and valuable source of information.

To our knowledge, this is the first study demonstrating that 7T fMRI can be used to consistently detect cortical and subcortical areas involved in sensory and motor tasks of the urogenital area in singe-subjects. We were able to reproduce significant image activation in multiple (subcortical and cortical) regions of interest in single subjects and demonstrate connectivity between specific areas involved in the tasks.

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