Sexually monomorphic maps and dimorphic responses in rat genital cortex
Gardiner, Jayne M.
Talbot, Zoe N.
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Mammalian external genitals show sexual dimorphism [1,2] and can change size and shape upon sexual arousal. Genitals feature prominently in the oldest pieces of figural art  and phallic depictions of penises informed psychoanalytic thought about sexuality [4, 5]. Despite this longstanding interest, the neural representations of genitals are still poorly understood . In somatosensory cortex specifically, many studies did not detect any cortical representation of genitals [7-9]. Studies in humans debate, if genitals are represented displaced below the foot of the cortical body map [10-12], or if they are represented somatotopically [13-15]. We wondered, what a high-resolution mapping of genital representations might tell us about the sexual differentiation of the mammalian brain. We identified genital responses in rat somatosensory cortex in a region previously assigned as arm/leg cortex. Genital responses were more common in males than in females. Despite such response dimorphism, we observed a stunning anatomical monomorphism of cortical penis and clitoris input maps revealed by cytochrome-oxidasestaining of cortical layer-4. Genital representations were somatotopic, bilaterally symmetric and their relative size increased markedly during puberty. Size, shape and erect posture give the cortical penis representation a phallic appearance pointing to a role in sexually aroused states. Cortical genital neurons showed unusual multi-body-part responses and sexually dimorphic receptive fields. Specifically, genital neurons were coactivated by distant body regions, which are touched during mounting in the respective sex. Genital maps indicate a deep homology of penis and clitoris representations in line with a fundamentally bi-sexual layout  of the vertebrate brain.
Author Posting. © The Author(s), 2015. This is the author's version of the work. It is posted here for personal use, not for redistribution. The definitive version was published in Current Biology 26 (2016): 106-113, doi:10.1016/j.cub.2015.11.041.
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