for reproduction, and the hypothalamus is the key brain area which regulates and coordinates the physiological and behavioural aspects of reproduction. Most of the time, the ventromedial nucleus of the hypothalamus (VMN) inhibits lordosis. But when environmental conditions are favorable and the female is in estrus, the estrogen hormone, estradiol, induces sexual receptivity by the neurons in the ventromedial nucleus, the periaqueductal gray, and other areas of the brain. The ventromedial hypothalamus sends impulses down axons synapsing with neurons in the periaqueductal gray. These convey an impulse to neurons in the medullary reticular formation which project down the reticulospinal tract and synapse with the neurobiological circuits of the lordosis reflex in the spinal cord (L1–L6). These neurobiological processes induced by estradiol enable the tactile stimuli to trigger lordosis. The mechanisms of regulation of this estrogen-dependent lordosis reflex have been identified through different types of experiments. 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, or exposure to stress during puberty. Specifically, stress can suppress the hypothalamic-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. In humans Lordosis behavior is non-functional in humans, although lordosis-like positions can be observed in women being mounted from behind. 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. 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". Previously, anthropologist Helen Fisher also speculated that when a human female wears high-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". Nonetheless, recent evidence has extended the effect of lordosis pose beyond a standing posture and high-heels, as it is indicated a sexual receptivity signal in other than standing postures of quadruped and supine in women. See also Ethogram