***A disclaimer: Sex addiction is a relatively new concept in science. I haven’t been able to find much research on the subject, so much of what is being said here is my interpretation of the current literature on sexual responsivity in humans.***

I’ve already mentioned that scientists are beginning to consider behavioral addictions (like gambling and sex) as being similar to drug addiction. We’ve also covered sex addiction on the site quite a few times.

Since we’d covered the addiction-brain effects of some of the major drugs’ (see here for opiates, crystal meth, and cocaine), I thought it’s time to write about the possible science behind sex addiction.

The sexual activity cycle

Scientists have divided human sexual interaction into 4 stages:

1. Desire – Represents a person’s current level of interest in sex. It is characterized by sexual fantasies and a desire to have sex.
2. Arousal – Includes a subjective sense of sexual pleasure accompanied by a physiological response in the form of genital vasocongestion, leading to penile erection in men and vulva/clitoral engorgement and vaginal lubrication in women.
3. Orgasm – Involves both central processes in the brain and extensive peripheral effects. Orgasm is experienced by the peaking of sexual pleasure, release of sexual tension, rhythmic contraction of the perineal muscles and pelvic reproductive organs, and cardiovascular and respiratory changes.
4. Resolution – The final stage of the normal sexual response cycle. There is a sense of release of tension, well being, and return of the body to its resting state.

Sex addicts don’t seem to have a problem with stage 3, and resolution is more like the end of sexual behavior. So we will focus the rest of our attention on the other stages 1 and 2.

Sex and neurotransmitters

While sex doesn’t involve the ingestion of substances, each of the above cycles does involve the release of many of the neurotransmitters we’ve already discussed (dopamine, serotonin, etc.).

In fact, there seem to be three major area in the brain that are activated during sex:

1. The Medial Preoptic Area (MPOA) – This is one of the areas where all the sensory inputs to the brain converge. This. This area is crucial for the initiation of sexual response – the move from desire to arousal. It is mostly the release of dopamine within this area that supports sexual responding. Animals with lesions here can’t  mount or thrust.
2. Paravantricular  (male) or ventromedial hypothalamus – These area are responsible for non-contact sexual responses. Dopamine is once again the main activating agent here.
3. The mesolimbic system – Important for the motivation towards anything “good” this system is also very involved in motivation for sex, a big part of the desire and arousal stages. As with drugs, it is the release of dopamine with this system that increases the motivation for sex.

We haven’t discussed the first two area much, and from my understanding, their functioning is relatively specific to sexual response. However, we’ve certainly mentioned the mesolimbic system. This is the same system involved in the brain’s processing of opiates, cocaine, methamphetamine, and essentially all other drugs. It is also the system in charge of food motivation.

As you can see, dopamine is an activating neurotransmitter for sexual response. Serotonin on the other hand, plays an inhibitory role in sex. Through its activity on a number of brain area, serotonin reduces desire, arousal, as well as the ability to orgasm. The increase of overall brain-serotonin levels is one of the main reasons for reduced sexual responsivity in individuals who are taking SSRI antidepressants.

What about sex addiction?!

Aside from a few specific authors (like P. Carnes), scientists still find themselves struggling with whether or not behavioral addictions should be considered similar to drug and alcohol addiction or whether they are examples of compulsive, or impulsive, behaviors. I personally believe that these all share more common features than we may yet realize.

Nevertheless, for addicts, the subjective experience of a substance, or behavioral, addiction is similar. It is an inability  to control a behavior in the face of repeated negative consequences that is often accompanied by a need for more and a reduced sensitivity to the act.

Given my recent reading on the brain processes involved in normal human sexual response, I’ve developed my own early theory about sex addiction:

Given that many of the same neurotransmitters are involved in the regulation of sex, it is my belief that sexual addicts or those experiencing sexual compulsions, fall into one of two categories that probably overlap to some extent:

1. Individuals who have reduced inhibitory capacity (like those with impulse control disorder, ADD, or ADHD for example). These individuals find themselves acting out relatively impulsive behaviors that others without such dysfunction seem to effortlessly control. Given what we know about impulse control disorders, it is no wonder that these individuals often find themselves engaging in more than one such behavior, including drug, sex, and other poossibly addictive activities.
2. Those who’ve had sex paired with a strong neurological response – Given the important role of dopamine in all rewarding activities (what scientists call appetitive response), it is very possible that two or more rewarding experiences that are linked may increase the brain’s response to any of the individual rewards.

Let me explain the last point: In neuroscience, there’s the concept that “Neurons that fire together wire together,” which is to say that events that happen at the same time, if they are strong enough, may form their own neural networks. If something strongly negative (like violence) happens in conjunction with sex, the experience might lower sex responsivity. However, if a strongly rewarding event happens at the same time, the link might serve to enhance response for both future sexual experiences and the linked event.  The people in the first group are likely to often fall into this category due to their use of psychoactive substances. Drugs release huge amounts of dopamine, which may then become linked with sexual response, making sex seeking as strong as drug seeking.

So that’s my take, for now, on sex addiction. Like other addictions, it has to do with the exposure to a very rewarding event that in a subset of individuals ends up developing an exaggerated response or an inability to control it. Since feeling of love and intimacy can often be just as rewarding, people often refer to themselves as love addicted, and not sex addicted.

Sources:

1) A. G., Resnick, & M. H. Ithman (2008). The Human Sexual Response Cycle: Psychotropic Side Effects and Treatment Strategies. Psychiatric Annals, 38, pp. 267-280.

2) E. M. Hull, D. S. Lorrain, J. Du, L. Matuszewich, L. A. Lumley, S. K. Putnam, J. Moses (1999) Hormone-neurotransmitter interactions in the control of sexual behavior. Behavioral Brain Research, 105, 105-116.