Male Urogenital System Mapped Onto the Sensory Cortex Thru Functional Magnetic Resonance Imaging: The nipple was found to project to the same cortical region as the genitals

Allen K, Wise N, Frangos E, et al. Male Urogenital System Mapped Onto the Sensory Cortex: Functional Magnetic Resonance Imaging Evidence. J Sex Med 2020;XX:XXX–XXX. https://doi.org/10.1016/j.jsxm.2019.12.007

Abstract
Introduction The projection of the human male urogenital system onto the paracentral lobule has not previously been mapped comprehensively.

Aim To map specific urogenital structures onto the primary somatosensory cortex toward a better understanding of sexual response in men.

Methods Using functional magnetic resonance imaging, we mapped primary somatosensory cortical responses to self-stimulation of the penis shaft, glans, testicles, scrotum, rectum, urethra, prostate, perineum, and nipple. We further compared neural response with erotic and prosaic touch of the penile shaft.

Main Outcome Measure We identified the primary mapping site of urogenital structures on the paracentral lobule and identified networks involved in perceiving touch as erotic.

Results We mapped sites on the primary somatosensory cortex to which components of the urogenital structures project in men. Evidence is provided that penile cutaneous projection is different from deep penile projection. Similar to a prior report in women, we show that the nipple projects to the same somatosensory cortical region as the genitals. Evidence of differential representation of erotic and nonerotic genital self-stimulation is also provided, the former activating sensory networks other than the primary sensory cortex, indicating a role of “top-down” activity in erotic response.

Clinical Implications We map primary sites of projection of urogenital structures to the primary somatosensory cortex and differentiate cortical sites of erotic from nonerotic genital self-stimulation.

Strength & Limitations To our knowledge, this is the first comprehensive mapping onto the primary somatosensory cortex of the projection of the components of the urogenital system in men and the difference in cortical activation in response to erotic vs nonerotic self-stimulation. The nipple was found to project to the same cortical region as the genitals. Evidence is provided that superficial and deep penile stimulation project differentially to the cortex, suggesting that sensory innervation of the penis is provided by more than the (pudendal) dorsal nerve.

Conclusion This study reconciles prior apparently conflicting findings and offers a comprehensive mapping of male genital components to the paracentral lobule. We provide evidence of differential projection of light touch vs pressure applied to the penile shaft, suggesting differential innervation of its superficial, vs deep structure. Similar to the response in women, we found nipple projection to genital areas of the paracentral lobule. We also provide evidence of differential representation of erotic and nonerotic genital self-stimulation, the former activating sensory networks other than the primary sensory cortex, indicating a role of top-down activity in erotic response.