Abstract
Female sexual arousal is a duarchy serving both procreative (reproduction) and recreative (pleasure) functions. Apart from a few isolated studies, the changes occurring in a woman's body during sexual arousal to orgasm received only scientific attention in mid-twentieth century.
A major landmark was the work of William Masters and Virginia Johnson (1954–1966), initially published in obscure American medical journals (1960–1963), but subsequently detailed in their unrefereed book Human Sexual Response (1966). Their phenomenological four-phased EPOR (excitation/plateau/orgasm/resolution) model of the human sexual response, created largely from naked eye observations, became almost iconic as no other laboratories were able to undertake critical confirmatory laboratory studies for many years.
By the mid-1970s, however, research workers in America and Europe had begun to measure various female psychosexual/physiological genital and body responses by objective techniques. Clinical studies with patients generated criticisms and weaknesses in the model. A ‘desire’ phase (D) was added and the plateau phase incorporated into the excitement phase creating the DEOR model. Later modifications involved splitting the desire phase into that arising spontaneously and that arising from sexual stimulation itself (reactive desire). The development and use of new techniques (vaginal photoplethsymography, the heated oxygen electrode, vaginal/rectal pressure recordings, endoscopy, ultrasound and Doppler imaging, intravaginal and intrauterine pH) allowed quantitative measurements to be obtained for blood flow, motility, ion and fluid movements and oxygen tensions.
Sexual arousal increases vaginal blood flow and the subsequent formation of vaginal lubrication (a neurogenic transudate) was found to be activated mainly by peripheral vasoactive intestinal peptide (VIP) with a small amount of nitric oxide (NO), while enhancement of clitoral blood flow used both VIP and NO.
Immunocytochemical analysis of the genital innervation revealed the sites and types of other neurotransmitters whose functions are still under study. New characterizations of genital structures (G-spot, peri-urethral glans, Halban's fascia) indicate erotic sites for the generation of sexual pleasure. Recently, visualization of genital structures by magnetic resonance imaging (MRI) during coitus has confirmed much of the previously described arousal phenomenology. Brain imaging, by PET or BOLD fMRI, is now able to show specific regional changes in brain blood flow during sexual arousal and orgasm, indicating what parts of the brain become involved although differences among the studies has not allowed a consensus to be agreed.
As the pharmaceutical industry is now actively interested in exploring treatments for female sexual dysfunction, we can expect to see significant progress in the study and understanding of female sexual arousal.