Although some authors dismiss the existence of a true VNO, there are many observations demonstrating a specific organ in the nasal mucosa which is not of a respiratory or olfactory nature 161719; thus, there should be no doubt that the VNO exists in humans. The VNO is often described as a blind-ending diverticulum in the septal mucosa opening via a depression, called the VNO pit, into the nasal cavity approximately 2 centimetres from the nostril 17.

On the basis of phylogenetic development, it would be surprising if all chemosensory communication has been lost. The fact that chemical communication does not seem to be a strong determinant of human behaviour is not a very strong argument for dismissing vomeronasal function, as implied by Keverne 20 and Meredith 12. The truth will likely be somewhere in between, i.e., the VNO is developed in adult humans, but has a significantly reduced function during phylogenetic development due to the more rapid development of other senses.

The VNO in humans does not have the classical appearance of a peripheral sensory ending, from which a bundle of nerve fibres originates and terminates in the central nervous system. It has been shown that adult human vomeronasal epithelium has a limited number of bipolar cells, positive for neuron-specific enolase, a specific marker for cells of neural origin 1721. In addition, a significantly higher density of unmyelinated axons has been observed in the mucosa below and near the human VNO, in comparison with other nasal mucosa 22. On the other hand, axons observed in the mucosa do not reveal the continuity or synaptic contact with the epithelial cells of vomeronasal nature 23.

The innervation of the VNO in animals is quite complex (for a review, see 13). In the human fetus, as in other species, the terminalis nerve, i.e., the zero cranial nerve, connects the VNO and the brain, acting as a pathway for migration of luteinizing hormone releasing hormone-producing neurons from the region of the VNO epithelium into the brain 242526. In addition, the terminalis nerve clearly persists in human adults 1227. Although it has not been shown that the terminalis nerve carries the axons of the VNO in adults, such speculation had often been published 122829.

There is electrophysiologic evidence of a response of the VNO to urine 18. Jacob and colleagues 3031 have reported changes in mood in humans elicited by chemicals extracted from human skin, including androstandione and estratetraenyl compounds. It has been reported that a local electrophysiologic response to the application of small amounts of the same substances, confined directly to the vomeronasal region and termed the electrovomeronasogram response 3233. In addition, responses from isolated cells and also a systemic response to such an application have been reported. Importantly, conventional odours did not elicit such response 32.

Several indirect reports of the presence of pheromone-like substances, influencing human behaviour, have been published (for a review, see 12). One of the most notable examples is a trend towards synchronization of menstrual cycles in women who live together 34. This function might be phylogenetically-based, i.e., the Lee-Boot effect, showing that group-housed female mice suppress estrus in order to conserve the energy normally put into cycling when there is no possibility of pregnancy 35. Conversely, in the presence of male stimuli, i.e., pheromones, group-housed females return to estrus cycling, the so-called Whitten effect 36. We can speculate that signalling pheromones might communicate information that alters an individual's probability of responding without necessarily evoking an immediate observable response in humans.

Although the VNO has more functions, probably the most important and most studied function of the VNO is its influence on sexual behaviour. Experiments on animal models have shown that the destruction or deafferentation of the VNO produces severe sexual behavioural deficits in both males and females (for a review, see 13). Based on a number of studies, the experiments of Bruce 37 most closely support our hypothesis. In these experiments, fertilised eggs failed to implant if a strange male was exchanged for the mating male in the cage of a female within 4 days of copulation. This effect was later shown to be dependent on the functional VNO 38. These experiments also indicated the important role of memory in the process of recognition of pheromones by the VNO. Recently, there has been a report showing that male mice deficient in Trpc2, an ion channel specifically expressed in VNO neurons and essential for transduction in the VNO, are impaired in sex-discrimination and male-male aggression, whereas females deficient in Trpc2 show a reduction in female-specific behaviour, including maternal aggression and lactating behaviour. In addition, the same results have been observed after the VNO is removed 39.

Our hypothesis presumes the VNO is lost during maxillary movement. In the case of maxillary impaction, we perform not only bony structure reduction, but also partial reduction of the inferior cartilagineous part of the nasal septum to prevent unfavorable and non-esthetic nose bending. During such a reduction, the VNO is electrocoagulated to control the bleeding from the nasopalatine artery, or even removed in toto. This statement is indirectly supported by the findings of Trotier et al. 17, who found a substantially lower number of VNOs in patients who underwent septal surgery of a different nature in comparison with healthy individuals.

To our knowledge, no comprehensive scientific study has analyzed the role of VNO loss during orthognathic surgery on the post-operative establishment of new relationships and mating behaviour of patients. However, several indirect reports have supported this statement. Jacobson 11 observed a 65% increase in positive influence on personality and self-confidence in patients after orthognathic surgery. In addition, 24% of patients stated an improvement in the establishment of relationships with the opposite sex 11. Williams et al. 40 showed that of patients who were not aware they had a problem in their social life, 24% stated that their social life was significantly improved after orthognathic surgery.

Importantly, social anxiety and depression rating indices of patients scheduled for esthetic surgery in the facial region, such as a blepharoplasty, face lift, or otoplasty, were significantly higher then the same indices of patients scheduled for orthognathic surgery. Thus, orthognathic patients present a significantly lower grade of psychological vulnerability 41. In addition, patients having orthognathic surgery seem to have fewer postoperative complications than patients having other cosmetic procedures 42. Pogrel and Scott 43 conclude that most orthognathic surgery patients are psychologically normal, so any routine psychological or psychiatric preoperative examination is not necessary. These data indicate the orthognathic patients are primarily not expected to change their personal lives dramatically. However, our experiences with more than 1000 patients who underwent combined orthodonthic and orthognathic treatment in our department indicate that the number of patients who changed their social life in terms of a change in existing mates or even became promiscuous is not as low as might be expected (Foltán, unpublished).