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Lordosis behavior (/lɔːrˈdoʊsɪs/[1]), also known asmammalian lordosis (Greek lordōsis, fromlordos "bent backward"[1]) orpresenting, is the naturally occurring body posture for sexual receptivity tocopulation present in females of mostmammals includingrodents,elephants, andcats. The primary characteristics of the behavior are a lowering of the forelimbs but with the rear limbs extended andhips raised,ventral arching of thespine and a raising, or sideward displacement, of thetail. During lordosis, the spine curvesdorsoventrally so that its apex points towards the abdomen.
Lordosis is a reflex action that causes many non-primate female mammals to adopt a body position that is often crucial to reproductive behavior. The posture moves thepelvic tilt in an anterior direction, with the posterior pelvis rising up, the bottom angling backward and the front angling downward. Lordosis aids in copulation as it elevates the hips, thereby facilitating penetration by thepenis. It is commonly seen in female mammals duringestrus (being "in heat"). Lordosis occurs during copulation itself and in some species, like the cat, during pre-copulatory behavior.[2]
The lordosisreflex arc is hardwired in the spinal cord, at the level of the lumbar and sacralvertebrae (L1, L2, L5, L6 and S1).[3] In the brain, several regions modulate the lordosis reflex. Thevestibular nuclei and thecerebellum, via the vestibular tract, send information which makes it possible to coordinate the lordosis reflex withpostural balance. More importantly, the ventromedialhypothalamus sends projections that inhibit the reflex at the spinal level, so it is not activated at all times.[4] Sex hormones control reproduction and coordinate sexual activity with the physiological state. Schematically, at thebreeding season, and when anovum is available, hormones (especiallyestrogen) simultaneously induceovulation andestrus (heat). Under the action of estrogen in the hypothalamus, the lordosis reflex is uninhibited.[5] The female is ready for copulation andfertilization.
When a male mammal mounts the female, tactile stimuli on the flanks, theperineum and therump of the female are transmitted via thesensory nerves in thespinal cord. In the spinal cord and lowerbrainstem, they are integrated with the information coming from the brain, and then, in general, anerve impulse is transmitted to themuscles via themotor nerves. The contraction of the longissimus and transverso-spinalis muscles causes the ventral arching of the vertebral column.[3]
Sexual behaviour is optimized for reproduction, and thehypothalamus is the key brain area which regulates and coordinates the physiological and behavioural aspects of reproduction.[6] Most of the time, theventromedial nucleus of the hypothalamus (VMN) inhibits lordosis. But when environmental conditions are favorable and the female is in estrus, theestrogenhormone,estradiol, inducessexual receptivity by theneurons in theventromedial nucleus,[7] theperiaqueductal gray, and other areas of thebrain. The ventromedial hypothalamus sends impulses downaxons synapsing with neurons in the periaqueductal gray. These convey an impulse to neurons in the medullaryreticular formation which project down thereticulospinal tract and synapse with the neurobiological circuits of the lordosis reflex in thespinal cord (L1–L6). These neurobiological processes induced by estradiol enable the tactile stimuli to trigger lordosis.
The mechanisms of regulation of thisestrogen-dependent lordosis reflex have been identified through different types ofexperiments. When the VMN is lesioned lordosis is abolished; this suggests the importance of this cerebral structure in the regulation of lordosis. Concerning hormones, displays of lordosis can be affected by ovariectomy, injections of estradiol benzoate and progesterone,[8] or exposure tostress during puberty.[9][10] Specifically, stress can suppress thehypothalamic-pituitary-gonadal (HPG) axis and therefore decrease concentrations of gonadal hormones. Consequently, these reductions in exposure to gonadal hormones around puberty can result in decreases in sexual behavior in adulthood, including displays of lordosis.[9]
While lordosis behavior has not been observed in humans, positions similar to lordosis can be seen in those beingmounted from behind, with the autonomous lordosis reflex replaced by a conscious decision to expose the vulva for penetration.[11]
In a 2017 study, using 3D models and eye-tracking technology it is shown that the slight thrusting out of a woman's hips influences how attractive others perceive her to be and captures the gaze of both men and women.[12] The authors argue "while reflexive lordosis posture is not exhibited by human females and receptivity is not passive or obligatory for them, a manifestation of lumbar curvature might serve as a vestigial remnant of proceptivity-/receptivity-communicative signal between men and women".[13] Previously,anthropologistHelen Fisher also speculated that when a human female wearshigh-heeled footwear the buttocks thrusts out and the back arches into a pose that simulates lordosis behavior, which is why high heels are considered "sexy".[14] Recent evidence has also supported the perception of sexual receptivity in women when arching the back in supine and quadruped poses.[15][16] Researchers have found that women perceive other women exhibiting this posture as a potential threat to their romantic relationship.[16]
