While in most animals, sexual behavior is a straightforward path for procreation, sex in humans takes various shapes, forms, and colors. It can be by yourself (masturbation) or with many people (orgies), it can be done with body parts besides the genitals (hands, mouths, or even toys), it can be between people of the same sex, and it can be in a plethora of social contexts (from one-night stands to marriage). Given this diversity, one must generalize a bit. However, scientists have generally agreed that sexual behavior unfolds in sequential stages, roughly pertaining to desire/arousal, stimulation/consummation, climax/orgasm, and resolution (Georgiadis & Kringelbach, 2012). While orgasm isn’t always reached by everyone, we focus on it here because of its important role in sexual intercourse as generally conceptualized.
Orgasm has been described as the epitome of pleasure, produced by a sequence of involuntary yet rhythmic pelvic muscle contractions (Georgiandis & Kringelbach, 2012). It also includes sharp peaks in cardiovascular arousal, loss of control, feelings of release, altered states of consciousness, and an altered sense of space and time (Holstege et al., 2003). Because orgasm usually happens in the context of a physical sexual stimulation it includes activation in the somatosensory pathways; specifically, the dorsal surface of the primary somatosensory cortex has been identified as neural representation of the penis and clitoris, the major pleasure organs (Georgiadis & Kringelbach, 2012). Orgasm correlates with increased activation in classic reward pathways, such as the ventral tegmental area (VTA) located in the midbrain. Studies in men and women found activation in important dopamine pathways in the VTA, including the A11 cell group, whose strongest projections are to the pelvic floor motorneurons, which induce the genital muscle contractions of orgasm (Georgiandis et al., 2006; Holstege et al., 2003). Curiously, the VTA is also activated during a heroin rush in an addict (Holstege et al., 2012). Woah.
Another part of the brain that is significantly activated during orgasm in both men and women is the cerebellum (Georgiandis & Kringelbach, 2012; Georgiandis et al., 2006; Holstege et al., 2003). Since the cerebellum is largely associated with motor control this activation could be due to the body movement involved in sexual intercourse and orgasm itself. Indeed, Georgiandis et al. (2006) concluded that this was the case due to similar activation during imitation of orgasm (one of the control conditions). Nevertheless, as I always like to remind my readers, this doesn’t discount it as part of the neurological activation of sexual behavior, intercourse, and orgasm. After all, in the real world, people move when they climax. However, other researchers have documented the cerebellum’s role in emotional processing (Middleton & Strick, 200), sexual arousal (Redouté et al., 2000) and reproductive behavior (Heath, 1972), suggesting a more complex connection beyond motor control. Interestingly, cerebellum activation has also been documented in heroin rushes (Sell et al., 1999) and lesions in it may cause blunting of affect (p9191 Hols), tying it to the reward pathways mentioned above.
We can also learn a lot from what isn’t activated. Sexual climax has repeatedly shown a marked decrease in activation in the brain regions associated with behavioral control, fear, and anxiety (Georgiandis et al., 2006). The frontal cortex is highly involved in moral reasoning and social judgement, both of which are suppressed during orgasm, leading to absence of moral judgement and self-referential thought (Georgiandis et al., 2006). This is perhaps why some people describe that they “lose themselves” during sex. I provide an anecdotal quote from the movie Don Jon (2013) to exemplify the point:
“[…] we’re making love. And while we’re doing it, all the bullshit does fade away, and it’s just me and her right there, and yeah I do lose myself in her. And I can tell she’s losing herself in me. And we’re just f—-n’… lost together.”
Deactivation of the temporal lobe in general, and the amygdala in particular, is consistently correlated with sexual arousal as well as orgasm (Georgiadis & Kringelbach, 2012). The amygdala is highly implicated in negative emotional reactions, while deactivation correlates with euphoric psychological states (Holstege et al., 2003). Therefore, deactivation in frontal lobe leads to behavioral release while deactivation in the amygdala leads to positive emotional influx, again tied to a drug rush (Breiter et al., 1997). This is compounded by the knowledge that midbrain activation, specifically dopamine release, is also an important part of the positive emotional reward of orgasm.
From this we can learn the mechanisms through which orgasms in particular, and sex in general, have a direct and important influence in our affect. So much so, in fact, that it has been documented that human beings actively use sexual intercourse to regulate their affect– what a way to destress, eh? (Shier, 2010). Of course, sex is a highly complex aspect of human life that cannot be reduced to merely orgasming. There are plenty of people that have never orgasmed yet still live a satisfactory sexual life; in part because sex is much more than an orgasm, and can be much more than the physical act. People have sex for various reasons, important among them being intimacy, emotional closeness, bonding, commitment, love, affection, acceptance, tolerance, and closeness (Basson 2000). But that’s a whole other story.
Note: while orgasm in men is, vastly, clearly measured by ejaculation, orgasms in women are more obscurely, but still reliably, assessed by measurement of rectal pressure. Who knew? Guess that’s why butt plugs are a thing.
Further reading:
Non-genital orgasms. It’s a thing.
Why Humans Have Sex. It’s for much more than pleasure.
References:
Basson, R. (2000). The female sexual response: A different model. Journal of Sex and Marital Therapy, 26, 51–65.
Breiter HC, Gollub RL, Weisskoff RM, Kennedy DN, Makris N, Berke JD, Goodman JM, Kantor HL, Gastfriend DR, Riorden JP, Mathew RT, Rosen BR, Hyman SE (1997) Acute effects of cocaine on human brain activity and emotion.Neuron 19: 591-611
Don Jon (2013). http://www.imdb.com/title/tt2229499/quotes
Georgiadis, J. R., Kortekaas, R., Kuipers, R., Nieuwenburg, A., Pruim, J., Reinders, A. A. T., & Holstege, G. (2006). Regional cerebral blood flow changes associated with clitorally induced orgasm in healthy women. European Journal of Neuroscience, 24(11), 3305-3316.
Georgiadis, J. R., & Kringelbach, M. L. (2012). The human sexual response cycle: Brain imaging evidence linking sex to other pleasures. Progress in neurobiology, 98(1), 49-81.
Heath, R. G. (1972). Pleasure and brain activity in man: Deep and surface electroencephalograms during orgasm. The journal of nervous and mental disease, 154(1), 3-18.
Holstege, G., Georgiadis, J. R., Paans, A. M., Meiners, L. C., van der Graaf, F. H., & Reinders, A. S. (2003). Brain activation during human male ejaculation. The Journal of Neuroscience, 23(27), 9185-9193.
Middleton FA, Strick PL (2000) Basal ganglia and cerebellar loops: motor and cognitive circuits. Brain Res Brain Res Rev 31: 236-250.
Redouté J, Stoleru S, Gregoire MC, Costes N, Cinotti L, Lavenne F, Le Bars D, Forest MG, Pujol JF (2000) Brain processing of visual sexual stimuli in human males. Hum Brain Mapp 11: 162-177.
Shrier, L. A., Koren, S., Aneja, P., & de Moor, C. (2010). Affect regulation, social context, and sexual intercourse in adolescents. Archives of sexual behavior, 39(3), 695-705.