It must be there, the penis and the clitoris are only the arms, armed with our desires. The real sex organ, the one who seduces and enjoys, it is our brain. It is he who pulls all the strings of our sexuality. It is logical, therefore, became, notably thanks to the increased performance of the medical imaging, the object of all desires of the sexologists and other neuroscientists.

Psychiatrist and researcher at Inserm (hôpital Paul-Brousse), the French Serge Stoléru* examines the desire and the excitement of sex for decades. In 1999, he was one of the first to make use of medical imaging to track the desire in the brain of healthy volunteers. In this case, he has used positron emission tomography (PET) scan, which measures metabolic activity through the injection of a radioactive tracer. In 2003, Stoléru has asked 15 men to watch a erotic film to note which areas of their brains responded – 8 volunteers with normal sexuality and 7 others the libido at half-mast. In this last group, it was observed a neuronal activity is abnormally high in the front of the medial prefrontal cortex. According to the interpretation of the researcher, the abnormal activity of this region removes the visual stimuli to their character exciting.

Excitement. Since then, many observations of this type have led to the conclusion that sexual desire is not confined to a single area of the brain. In fact, many regions are involved, forming a network between them. “Our team has proposed a model neurophénoménologique of sexual arousal,” explains Serge Stoléru. By phenomenology, we mean the subjective experience by the person. It includes cognitive aspects (e.g., “I find this person desirable”), motivational aspects (“I feel the urge to get close to it”), emotional aspects (“I hope I’ll please him too “) and aspects that are tangible (“I feel my heart that beats louder”). Our model attempts to match each of these aspects with the activation of specific areas of the brain. ” 

The desire to the sexual act itself, there is a not huge (or not) to cross. The work of Serge Stoléru, but also those of other teams show that some brain regions to inhibit and control the desire or its expression in behavior. “Located at the base of the brain, the caudate nucleus seems to be involved in the inhibition of the passage to the act when a person feels desire but that the circumstances and the social context are that such an act would be inappropriate,” says the researcher.

Cascade of events. The sight of his partner in the process of undressing, an exchange of kisses, foreplay trigger a cascade of reactions in the brain. If no inhibition occurs, then the spinal cord receives the order to trigger an influx of blood into the penis, in the clitoris . Note, however, that in the quadriplegic, whose spinal cord is broken, the sexual organs can short-circuit the brain. Stimulated, they send signals directly to the spinal cord so that it triggers erection or lubrication.

The anthropologist american Helen Fisher, of the Institute of Kinsey, also examined the brain activity of someone who is in love. “Like hunger, thirst or the maternal instinct, the love is a physiological need “, she notes in her book ” Why we love ? “(Robert Laffont). The feeling of love is deeply inscribed in the structure and chemistry of the brain. The researcher links the desire to testosterone, the feeling of love to the dopamine and attachment with oxytocin and vasopressin.

” Little death “. The rise of desire leads sometimes, but not always, on the orgasm, the famous ” little death “. What happens in the brain of the man and the woman ? The enjoyment borrows the same circuits in the one and in the other ? There has fifteen years, the neurologist Dutch Gert Holstege asked the companions of the 11 young men to masturbate up to the enjoyment for he could observe their brain during a PET scan. At the time of the greatest excitement, the ventral tegmental area is activated. Located in the centre of the brain, it is an essential link in the reward circuit by producing dopamine, a hormone of pleasure. In short, the orgasm triggers the same reward circuitry as a pleasure of any kind, be it the food or the drug. Another observation of the neurologist during ejaculation : a decrease of the activity of the amygdala, the area involved in fear and vigilance. Repeating this experiment with 13 women, Gert Holstege had a little surprise for you : a radio silence for the greater part of the cortex devoted to emotions and fear. “The deactivation of these areas may be critical to reaching orgasm. If you are very anxious, it is very complicated to have sexual relations, ” note the neurologist. In contrast, during the love, the cerebellum, which manages the movement is very active.

However, we must be wary of hasty conclusions, drawn from a small number of observations. The neuroscientist Nan Wise at Rutgers university, in New Jersey, has observed, on the contrary, that the areas controlling memory, decision-making and emotions, as well as those responsible for sending information to the rest of the body turbinaient to the maximum. Another study conducted by the American Barry Komisaruk, from the same university, says that a woman can climb the walls without a sexual partner, or even masturbation. Only the mental account. He highlighted among women who have been victims of a spinal cord injury. When he asked them to use their imagination to masturbate mentally, some have come to enjoy. The same areas of the brain that in a woman harmless have reacted.

Increase the pleasure. in Short, there is still much to learn about the functioning of our biggest sexual organ. But a day will certainly come where the lack of libido and frigidity can be decrypted and cared for by an action on the brain. And thus increase the sexual pleasure ? Serge Stoléru is wary : “research to increase the sexual desire should be reserved exclusively for cases of the disorder pathological desire, for which people come to seek help from a clinician. It is necessary to solve the important ethical questions they pose. “So far, tracks are promising. “Today there are techniques, such as transcranial magnetic stimulation, which can increase or decrease the activity of certain brain regions. We can therefore, in theory, to imagine that the brain regions involved in sexual desire are the subject of this stimulation. ” 

The endocrinologist Waljit Dhillo, of imperial College London, was injected in 29 young people volunteers of kisspeptin. Identified in 2005, this hormone stimulates, in particular, the production of testosterone. Using functional MRI, the researchers found that kisspeptin activates the structures of the deep-brain, involved in sexual desire and the system of the reward, but also those which control the disinhibition of sexual. In short, the kisspeptin could be this conductor, which stimulates the pleasure while stimulating the reproductive organs. Waljit Dhillo would like to now verify that it plays the same role in women. His job wisely could help some couples on the evil of child design§ 

* Serge Stoléru is the author of” A brain named desire ” (Odile Jacob).

THIERRY BERROD, MONA LISA PRODUCTION/SPL/PHANIE

On the same subject, sexuality in France

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