Cutting-edge research has demonstrated the benefits of using a powerful technology to map or record brain activity during sexual arousal. Functional magnetic resonance imaging (fMRI) is a research and diagnostic device that provides images of the soft tissues of the brain, blood flow in various brain regions, and indications of which regions of the brain activate or "light up" (via accelerated neuron firing) during various mental processes, such as thinking or emoting. Researchers have demonstrated that fMRI can be used to record brain activity during sexual arousal of either sex (Arnow et al., 2002; Holstege et al., 2003; Karama et al., 2002; Whipple & Komisaruk, 2006).
In one study, male and female subjects viewed erotic video clips while undergoing fMRI scanning (Karama et al., 2002). Brain activation in regions of the limbic system, especially pronounced in the amygdala, was observed in both sexes. In another experiment, men viewed erotic video clips while being scanned in an MRI machine. Brain activation during sexual arousal was observed in these research subjects, especially in the hypothalamus and cingulate gyrus, both limbic system structures (Arnow et al., 2002). Another study used fMRI scanning to record brain activity during women’s orgasmic responses. Heightened levels of brain activation were observed in several areas of the limbic system, including the hypothalamus, amygdala, hippocampus, and cingulate gyrus (Komisaruk et al.,
2006; Whipple & Komisaruk, 2006).
The results of these and similar studies demonstrate that fMRI technology offers an excellent tool for monitoring the brain during sexual arousal and response. Clearly this technology holds great promise for advancing our understanding of the role of the brain in our sexuality.
Robert Heath (1972) experimented with limbic system stimulation in patients suffering from various disorders. He theorized that stimulation-induced pleasure would prove to have some therapeutic value. One patient, a man with an emotional disorder, was provided with a self-stimulation device that he used up to 1,500 times per hour to administer stimulation to an area in his limbic system. He described the stimulation as producing intense sexual pleasure, protesting each time the unit was taken away from him. Another patient, a woman with an epileptic disorder, reported intense sexual pleasure and experienced multiple orgasmic responses as a direct result of brain stimulation.
Several studies have implicated the hypothalamus in sexual functioning. When certain parts of the hypothalamus are surgically destroyed, the sexual behavior of both males and females of several species can be dramatically reduced (Paredes & Baum, 1997). One region in the preoptic area of the hypothalamus, the medial preoptic area (MPOA), has been implicated in sexual arousal and sexual behavior. Electrical stimulation of the MPOA increases sexual behavior, and damage to this area reduces or eliminates sexual activity in males of a wide variety of species (Stark, 2005). Opiate drugs, such as heroin and morphine, have a suppressive effect on the MPOA and are known to inhibit sexual performance in both sexes (Argiolas, 1999).
Sexual Arousal and Response
Certain naturally occurring brain substances, called neurotransmitters (chemicals that transmit messages in the nervous system), are also known to influence sexual arousal and response by their effect on the MPOA. One of these transmitter substances, dopamine, induces neural activity in the MPOA that has a facilitatory effect on sexual arousal and response in males of many species (Giargiari et al., 2005; Wilson, 2003). Furthermore, testosterone is known to stimulate the release of dopamine in the MPOA in both males and females (Wilson, 2003). This finding indicates one possible mechanism by which testosterone stimulates libido in both sexes.
In contrast to the facilitatory impact of dopamine on sexual behavior, the neurotransmitter serotonin appears to inhibit sexual activity. Male ejaculation causes a release of serotonin in both the MPOA and the lateral hypothalamus, an area on the sides of the hypothalamus. This released serotonin temporarily reduces sex drive and behavior by inhibiting the release of dopamine (Hull et al., 1999). Serotonin also suppresses sexual arousal by blocking the action of oxytocin (Wilson, 2003). Humans who suffer from depression are often provided antidepressant medications called selective serotonin reuptake inhibitors (SSRIs). These drugs, whose effect is to increase serotonin levels in the brain, often interfere with libido and sexual response. Research has shown that SSRIs diminish genital sensitivity and reduce orgasmic capacity in both sexes (Bahrick, 2008).
Collectively these various findings provide strong evidence that dopamine facilitates sexual arousal and activity in women and men, whereas serotonin appears to provide an inhibitory effect on both sexes.
It is doubtful that researchers will ever find one specific "sex center" in the brain. However, it is clear that both the cerebral cortex and the limbic system play important roles in initiating, organizing, and controlling human sexual arousal and response. In addition, the brain interprets a variety of sensory inputs that often exert a profound influence on sexual arousal. We examine this topic in the next section.