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Lordosis behavior, also known as mammalian lordosis (Greek lordōsis, from lordos "bent backward") or presenting, is a body posture adopted by some mammals including humans, elephants, rodents, felines and others, usually associated with female receptivity to copulation. The primary characteristics of the behavior are a lowering of the forelimbs but with the rear limbs extended and hips raised, ventral arching of the spine and a raising, or sideward displacement, of the tail. During lordosis, the spine curves dorsoventrally so that its apex points towards the abdomen. In human physiology, the term "lordosis" is sometimes used to describe an abnormal forward curvature of the spine in the lumbar region.
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 the pelvic 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 the penis. It is commonly seen in female mammals during estrus (being "in heat"). Lordosis occurs both during pre-copulatory behavior and during copulation itself.
Lordosis brain circuits are connected with other neural circuits, especially the olfactory and reward systems.
The main phases of reproductive behavior are:
- Odors, especially pheromones, make it possible to exchange sexual signals between potential partners.
- Olfactory circuits (red arrows in the above diagram) make it possible to recognize the partner of the opposite sex and to trigger sexual arousal, which induces vaginal lubrication, erection and copulation.
- When the male mounts the female, the male's tactile stimuli on the female's rump trigger the lordosis reflex.
- The lordosis circuits cause the ventral arching of the spine, which elevates the hips and presents the vagina to the male, thereby facilitating penetration by the penis.
- The tactile contact between the penis and the genital area triggers the reflex movements of the male's pelvis (pelvic thrusts), then intromission. After intromission, the penis's movements in the vagina trigger the reflex of ejaculation.
- Tactile stimulation of the clitoris (and the penis for the male) during copulation is transmitted to the brain (blue arrows).
- Activation of the reward system induces learning which optimizes copulation, particularly by the development of sexual motivation. Moreover, olfactive, auditory and visual signals perceived during the copulation may by conditioning become sexual signals, which optimizes the innate pheromonal signals.
There is thus, in the innate neurobiological organization of the organism, a true heterosexual reproductive behavior in non-primate mammals.