It is a cliché that the brain is the "largest sex organ," but the repetition of the phrase doesn't make it any less true. The mechanics of its role during sex are less obvious and less well understood than that of the body's other sex organs, but by using brain imaging scans, neuroscientists have begun to get a sense of what parts of the brain light up during sex, especially at the moment of orgasm.
In his Big Think interview, Rutgers psychologist Barry Komisaruk, a pioneer of neuroscientific sex studies on the female orgasm, told us what science now knows about "la petite mort." One early study of orgasms, he explains, suggests that the subjective experience of orgasm is very similar between men and women. Despite having different anatomies, men and women seem to be hard-wired to experience sexual pleasure in the same way. But does this translate to a similarity in the brain?
Newer brain imaging technology has allowed neuroscientists to test just this. In 2003 Dutch neuroscientist Gert Holstege used brain scans to see what parts of the brain were activated in both men and women during orgasm. First he used PET brain scans to study men during that most intimate of moments. What he discovered was that the part of the brain with the greatest activation was a structure called the ventral tegmental area (VTA), which, not surprisingly, is responsible for the release of dopamine. Dopamine, as discussed earlier this week as part of Big Think's month of Going Mental, is the neurotransmitter most essential for the brain's reward circuit, the same circuit that is exploited by drugs like cocaine and heroine. This accounts for both the fact that heroin addicts experience orgasmic pleasure as a result of their drug use as well as the fact that heroin addicts have suppressed sex drives, likely because this region is already stimulated so intensely by the heroin. But sex, unlike drug use, is an evolutionarily advantageous behavior: "Because ejaculation introduces sperm into the female reproductive tract, it would be critical for reproduction of the species to favor ejaculation as a most rewarding behavior," Holstege wrote in The Journal of Neuroscience. He also found a decrease in activity of the amygdala, the seat of vigilance and fear, during ejaculation.
But when Holstege tested women, he found something surprising. Much more so than men's brains, female brains go mysteriously silent during orgasm. In particular, the left lateral orbitofronal cortex and the dorsomedial prefrontal cortex, areas involved in self-control and social judgment, respectively, are deactivated. Brain activity also fell in the amygdala, suggesting a similar, albeit more drastic, drop in vigilance and emotion as in men. "At the moment of orgasm, women do not have any emotional feelings," Holstege was quoted as saying.
Komisaruk's research suggests another way that women's brains are different than men's when it comes to sex: some women can "think themselves off"—induce orgasm without any physical stimulation. This special talent, he says, comes from the fact that "when women think about their finger being stimulated, or they think about their toe being stimulated, or they think about their clitoris being stimulated, or their nipple, the corresponding part of the body, the representation of it in the sensory cortex...is actually activated just as if they are really being stimulated physically." This knowledge might help make sex more pleasurable for women, especially the 10% of women who report they have never experienced an orgasm and the 50% who have trouble getting aroused. "The question is, if we can see our own brain activity in near real time in specific regions, can we voluntarily increase the activity of that part of the brain just by thinking about it," Komisaruk asks.
Komisaruk also identified an activation of the paraventricular nucleus of the hypothalamus, which governs the release of oxytocin, a hormone involved in increasing trust and human bonding. This process occurs in three stages, writes Komisaruk: "The PVN neurons secrete oxytocin, which is stored in the posterior pituitary gland; vaginal or cervical stimulation releases the oxytocin from the posterior pituitary gland into the bloodstream, in the Ferguson Reflex; and orgasm releases the oxytocin into the bloodstream."
Dopamine is the chemical responsible for the euphoria of orgasm. During sexual climax, the VTA in the midbrain releases dopamine, which travel to the nucleus accumbens, the major structure of the brain's reward circuit. Dopamine also travels to several other parts of the brain, including the prefrontal cortex, the problem-solving are of the brain. Scientists speculate this connection may be related to the pleasure derived from solving problems. Dopamine also travels to the hippocampus and amygdala, which together govern memory. This connection might create memories that remind a person which previous behaviors resulted in neurological reward.
—"Functional MRI of the Brain During Orgasm in Women," a 2005 study published by Barry Komisaruk and Beverly Whipple
—"Brain Activation during Human Male Ejaculation," a study by Gert Holstege published in The Journal of Neuroscience in 2003