Single subject and group whole-brain fMRI mapping of male genital sensation at 7 Tesla

Abstract

Processing of genital sensations in the central nervous system of humans is still poorly understood. Current knowledge is mainly based on neuroimaging studies using electroencephalography (EEG), magneto-encephalography (MEG), and 1.5- or 3- Tesla (T) functional magnetic resonance imaging (fMRI), all of which suffer from limited spatial resolution and sensitivity, thereby relying on group analyses to reveal significant data. Here, we studied the impact of passive, yet non-arousing, tactile stimulation of the penile shaft using ultra-high field 7T fMRI. With this approach, penile stimulation evoked significant activations in distinct areas of the primary and secondary somatosensory cortices (S1 & S2), premotor cortex, insula, midcingulate gyrus, prefrontal cortex, thalamus and cerebellum, both at single subject and group level. Passive tactile stimulation of the feet, studied for control, also evoked significant activation in S1, S2, insula, thalamus and cerebellum, but predominantly, yet not exclusively, in areas that could be segregated from those associated with penile stimulation. Evaluation of the whole-brain activation patterns and connectivity analyses indicate that genital sensations following passive stimulation are, unlike those following feet stimulation, processed in both sensorimotor and affective regions.

Figure 1

Single subject cortical activation patterns. Single subject activation maps (p < 0.05 FWE) from all individuals (n = 13) displayed on inflated anatomical images showing top-view. Legend in bottom-right corner indicating task specific color codes.

Figure 2

Group cortical activation patterns. Group activation maps (p < 0.005 uncorrected for multiple comparisons; n = 13) displayed on an inflated MNI template showing lateral, medial and top view. A coronal section from the MNI template (y = −36) is shown in the bottom-left corner, where the penile shaft is clearly located lateral to the feet in S1. Legend in the bottom-right corner indicating task specific color codes.

Figure 3

Single subject and group cerebellar activation patterns. Single subject activation maps from all individuals (p < 0.001 uncorrected for multiple comparisons) displayed on axial sections containing maximum number of representations. Group activation maps (p < 0.005 uncorrected for multiple comparisons, n = 13) displayed on sagittal and axial sections from the MNI template (x and z-coordinates in top-left corner indicate position in MNI space). Legend in bottom-right corner indicating task specific color codes.

Figure 4

Mean connectivity matrix for penile shaft activation displaying connectivity between regions of interest. Individual connectivity matrices of 9 single subjects were first generated using a Pearson’s correlation coefficient, and subsequently used to generate a mean connectivity matrix. Regions of interest included are labeled along axes.

Figure 5

Mean connectivity matrix for left (A) and right (B) foot activation displaying connectivity between regions of interest. Individual connectivity matrices of 10 single subjects were first generated using a Pearson’s correlation coefficient, and used to generate a mean connectivity matrix. Regions included are labeled along the axes.

Figure 6

Mean signal intensity (in arbitrary units, a.u.) over time (in seconds, s) superomedial in S1 during tactile stimulation of the penile shaft and feet. The stimulation paradigm included 10 blocks (stimulation versus rest) each lasting 60 seconds with an additional rest block at the start resulting in a total scan duration of 620 seconds per task. For viewing purposes, curves were centered around separate baseline values. All timeseries were normalized prior to averaging across subjects. The shaded error bars indicate the standard error over subjects.