Brain Sex in Men and Women – From Arousal to Orgasm
Sex is all in our heads, quite literally. Our brains are involved in all steps of sexual behavior and in all its variations, from feelings of sexual desire and partner choice, to arousal, orgasm and even post-coital cuddling.
Now, with hundreds of neuroimaging studies on human sexual behavior, results from these studies are finally being integrated for meta-analysis, allowing for improved precision in identifying activated brain areas. This article reveals the neural model of sexual arousal, culminating in orgasm research and the surprising similarities, and marked differences, between the sexually aroused brain of men and women.
The neural model of sexual arousal
The meta-analysis of 58 neuroimaging studies of mainly hetero- and homosexual men viewing erotic pictures and/or videos, and to a lesser extent heterosexual women, that resulted in the development of a four-component neurophenomenological model of sexual arousal. The four components are described below.
Cognitive component: perception and appraisal
The first stage of the model is the cognitive component, where one perceives the sexual visual stimulus and judges its sexual nature and then focuses attention accordingly, which may lead to the mental rehearsal of performing a sexual act. Parts of the ventromedial prefrontal cortex (vmPFC), through connectivity to the limbic reward and emotion systems, as well as areas involved with our senses, are thought to be promote the recognition and grading of the sex appeal of a stimulus.
This subsequently alters a persons focus of attention to the sexual stimulus, creating the high strength of activity observed in visual processing areas of the temporal and occipital lobes. This includes the extrastriate body, which is a specialized area for perceiving the human body. As the vmPFC is well-connected to all five sensory modalities it is reasonable to assume it would similarly influence the focus and perception of the other senses; taste, smell, touch and hearing.
Emotional component
The amygdala is involved in evaluating the emotional content of a sexual situation, which, along with the vmPFC, helps to control sensory processing and attention. This emotional processing of the amygdala is well connected to motivational areas of the brain, therefore guiding sexual behavior.
On the other hand, in experiments involving manual physical arousal or during orgasm, deactivation of the amygdala was found. Interestingly, similar deactivations are thought to contribute to hypersexuality and indiscriminate sexual behavior in individuals with Kluver and Bucy syndrome.
The emotional component is not considered strictly emotional as such, as it also involves the more physical feelings of pleasure that one experiences the more turned on one becomes. This includes activations in the left somatosensory cortex that are neurally connected to the genitalia.
Motivational component
Intertwined with the emotional component is the motivational component of the sexual arousal model, and as such heavily involves the dopamine dependent limbic system. Of these areas the most consistently activated across the studies is the anterior cingulate cortex (ACC), the thalamus, the parietal cortex and the hypothalamus.
Processing of these limbic areas is what directs behavior towards a sexual goal, which includes sexual urges, desires and feelings of reward. While stimulating monkey’s ACC causes an erection, it seems that in humans, the striatum is the only area currently found to be specific to the emotional-motivational component of sexual arousal alone, as opposed to general emotional arousal.
Physiological component
Heart racing, blood pressure soaring, genital responses and hormonal changes are all part of the parcel when it comes to the physiological state of being sexually aroused, preparing the body for sex. This physiological sexual readiness is also controlled by the brain.
According to the model, activation in the ACC, anterior insula, putamens and hypothalamus participates in generating autonomic and hormonal responses to sexual arousal. In men, the hypothalamus, through its control of the sympathetic and parasympathetic nervous systems, is most associated with male sexual arousal and penile responses to sexual stimuli.
Inhibition
Finally, inhibitory processes are thought to keep us behaving appropriately and not succumbing to urges that may be unacceptable to a potential partner. Conversely, over-inhibition may prevent sufficiently gratifying sexual encounters. Inhibitory regions include areas of the temporal lobes, ACC and vmPFC. Lesions in these regions are known to cause socially disruptive and excessive pleasure-seeking behavior.
Men versus women: not that different
Although male heterosexual studies have dominated the literature, broadly speaking, active brain areas during sexual arousal are highly similar for both men and women of all sexual orientations. Studies comparing sexual arousal in the brains of men and women generally note that women have weaker responses to the visually erotic stimuli that are common of sexual neuroimaging studies.
However, relatively few studies have compared male and female participants and although discrete sex differences in sexual brain activation clearly exist, they have varied across studies. More thorough research will be necessary to determine which results are reliable and whether other sex differences exist.
Context is key
Some recent studies indicate that the context and format of the visual sexual stimuli commonly used in neuroimaging studies might not be enough to get the average woman as equally fired up as the average man is when presented with visually erotic stimuli – women are sexually more complex creatures. In fact, women in some studies, have been shown to have a stronger neural response than men, albeit when smelling pheromones in the sweat of sexual partners.
Recently, when comparing men and women’s responses to erotic videos that either set the mood (having an emotional component and story) or physically set the scene (where sexual intercourse and genitalia where directly displayed) women’s responses were stronger for the mood type videos, whereas the men preferred the physical type videos. Research also indicates that women have a more profound temporal component to sexual arousal than men. Although currently poorly understood, the least sexually aroused time is considered the follicular phase, a potentially fertile period, enabling females to be selective and cautious when committing to a sexual encounter in this period.
Sexual preference
Where men show a robust neural reaction in brain regions involved in visual attention, motivation, and genital arousal to erotic stimuli depicting one sex, and very little reaction in these regions to erotic stimuli depicting the other sex, women show more similar reactions to both types of erotic stimuli. In other words, both heterosexual and homosexual men have stronger activation for images of their preferred sex than their non-preferred sex. In contrast, women have more similar reactions to both sexes and do not differ between sexual orientations.
Orgasm and brain activation patterns
Similarly, and in spite of the general perception that male orgasms are from Mars and female orgasms are from Venus, men and women again have similar brain activity patterns during orgasm. It is worth nothing that although orgasm studies show similar brain activity patterns, discrete activations and deactivations vary depending on how orgasm was achieved.
In both sexes, four different nerve systems connect the genitals to the brain, which, with a stimulation surge, shoot excitatory signals to the brain upon reaching orgasm. Subsequently, regions all over the brain appear to light up, while the vmPFC and amygdala are shut down —reportedly like taking heroin. The deactivations are considered to constitute the temporary sexual disinhibition required for an orgasm to take place, ‘robbing’ us of the voice of reason that controls our behavior and critical thinking.
Neurochemical love buzz
And we can’t forget the neurochemical cocktail that results in a “cloud-nine” buzz both during and after orgasm. How men and women’s bodies react to this chemical mash, including oxytocin, prolactin and endorphins, is perhaps where the sexes differ most profoundly and is shrouded in confusion and controversy. Many functions are attributed to this neurochemical rush from bonding and cuddling behavior, to enhancing the chances of successful reproduction.
Future implications for neuroimaging and the brain on sex
Research has essentially revealed the tip of the iceberg when it comes to understanding sexual arousal in the brain. Developing and expanding on the neural model of sexual arousal should provide valuable insights into the cognitive, emotional, motivational and physiological aspects of sexual arousal. Seeing as these studies lie at the boundaries between the mental and physical, further developments will surely shed light on Freudian theories of sexual desires.
More importantly, gaining a deep understanding of the neural underpinnings of sexual arousal will ultimately contribute to solving public health problems such as sexual disorders and sexual offending. We have much to learn.
Written by Carla Clark, PhD | May 20, 2014
