Sexual arousal
The physical stimulation of an erogenous zone or acts of foreplay can result in arousal, especially if it is accompanied with the anticipation of imminent sexual activity.
Scientists from McGill University Health Centre in Montreal (in Canada) used the method of thermal imaging to record baseline temperature change in genital area to define the time necessary for sexual arousal.
There are many reasons why a person fails to be aroused, including a mental disorder, such as depression, drug use, or a medical or physical condition.
Physical or psychological stimulation, or both, leads to vasodilation and the increased blood flow engorges the three spongy areas that run along the length of the penis (the two corpora cavernosa and the corpus spongiosum).
[9] Equally, a male erection can occur during sleep (nocturnal penile tumescence) without conscious sexual arousal or due to mechanical stimulation (e.g., rubbing against the bed sheet) alone.
[10] As sexual arousal and stimulation continues, it is likely that the glans or head of the erect penis will swell wider and, as the genitals become further engorged with blood, their color deepens and the testicles can grow up to 50% larger.
Repeated or prolonged stimulation without orgasm and ejaculation can lead to discomfort in the testes (corresponding to the slang term "blue balls"[12]).
After ejaculation, men usually experience a refractory period characterized by loss of their erection, a subsidence in any sex flush, less interest in sexual activity, and a feeling of relaxation that can be attributed to the neurohormones oxytocin and prolactin.
[19][20] Some suggest that psychological sexual arousal results from an interaction of cognitive and experiential factors, such as affective state, previous experience, and current social context.
[25][26] There are reported differences in brain activation to sexual stimuli, with men showing higher levels of amygdala and hypothalamic responses than women.
The basic incentive-motivation model of sex suggests that incentive cues in the environment invade the nervous system, which results in sexual motivation.
Motivation and behaviour are organized hierarchically; each are controlled by a combination of direct (external stimuli) and indirect (internal cognitions) factors.
[34] This model created by John Bancroft and Erick Janssen, previously at the Kinsey Institute, explores the individual variability of sexual response.
[36] Female focus groups found that the context of the emotional relationship between sexual partners was not fully represented in the original SIS/SES questionnaire.
[38] The majority of studies investigating sexual functioning use heterosexual participants exclusively, limiting the generalizability of the dual control model.
Ivan Tarkhanov showed, in experiments on cutting and artificial emptying of the seminal vesicles, that the latter played the crucial role in the generation of sexual excitement in frogs.
Proceeding from these experimental results, Tarkhanov put forward a hypothesis that filling and evacuation of the seminal vesicles were the main biological cause, which led to sexual arousal and its disappearance in humans and other mammals.
The study performed by Beach & Wilson (University of California, Berkeley) in 1964 discovered that these glands do not participate in the regulation of sexual arousal of male rats in the similar manner.
[46]: 95 The "psychohydraulic model of sexuality" has been formulated most definitely in psychoanalysis: The instinct causes tensions within the central nervous system, which spread out over the whole being; it is urgent and irresistible in nature and constantly repeats itself. ...
[49] Sexual arousal in women is characterized by vasocongestion of the genital tissues, including internal and external areas (e.g., vaginal walls, clitoris, and labia).
[58] Other researchers argue that since the research is done on people who volunteer to be studied, the observed levels of category specificity may not represent the population, that there may be different cultural expectations of sexual interests being linked to genital arousal that make men with non-category specific genital arousal less likely to appear as test subjects.
There researchers also argue that the assumption that men are always sexually interested in what causes genital arousal removes its own falsifiability by explaining all contradictory data away as "denial", making the theory untestable.
For instance, men and women alike are capable of classifying sex acts as sexual no matter if they find them appealing or not, making a genital response to unappealing erotic stimuli a single mechanism step.
These neurologists cite the existence of significant volunteering bias among men but not women in erotica research, in particular that the overrepresentation of erectile dysfunction yet underrepresentation of sexuality-related shame in volunteers is consistent with the hypothesis that genital response to both sexual relevance and appeal allows for a stronger erectile function than response only to appeal and that a majority of the male population are ashamed of their responses to unappealing stimuli, accounting for the discrepancy between the report from most heterosexual couples that male erection is faster than female lubrication and the appearance on pletysmography volunteers that female lubrication is at least as fast as male erection.
Arousal non-concordance is when there is no link, for example, in morning erection, which happens both with men (nocturnal penile tumescence) and women (nocturnal clitoral tumescence), or in cases of rape where research confirms reports of an arousal non-concordance orgasm or orgasm alike event can take place – presumably as a measure to protect the internal organs of the vagina.
There may be a difference in women's ability to perceive internal versus external genital engorgement subjectively, as measured by vaginal photoplethysmography (VPG) and thermography respectively.
Chivers and colleagues[65] found that men's and women's concordance was more similar when thermography was used as a measure of genital sexual arousal than when VPG was used.
However, few studies using thermography have been conducted and further research is required to determine whether the gender difference in concordance is a measurement artifact or a true phenomenon.
[68] Inconsistent study results point to the idea that while testosterone may play a role in the sexuality of some women, its effects can be obscured by the co-existence of psychological or affective factors in others.
Smith has also written extensively on the "seminal fluid swapping theory" logistic application of the assortment of alleles as a more accurate synthetic depiction of the Hardy–Weinberg principle in cases of severely interbreeding populations.
