In recent years, neuroscience discoveries about the reward system and human sexuality have shed new light on both problematic and healthy sexual behavior. As can be expected with any new paradigm, however, some doubtful neuroscience claims have also appeared in the media. As a neurosurgeon and the author of several papers on problematic sexual behavior and the appetite/reward mechanisms of the brain, I sometimes help to correct these misunderstandings. Here are a few examples that might be of interest to our readers.
ERROR #1 - “Dopamine does not underlie addiction”
Some peculiar claims about dopamine have appeared in recent months, such as “If you want to make an argument that porn is addictive, you can, but if you're relying on dopamine to do it. lol, you're wrong” and “Please stop calling dopamine an addictive rewarding neurochemical.”
Dopamine plays many benign roles in our physiology, such as facilitating movement and choices. However, all experts in the fields of addiction or neuroscience acknowledge the central role of dopamine in addiction.
In fact, addiction cannot develop without high, but brief, bursts of dopamine in response to an addictive substance or activity. As experts Volkow and Koob explained in a recent paper, these dopamine surges elicit reward signals at a cell receptor level, which then trigger so-called Pavlovian learning. The molecular mechanisms that facilitate this process appear similar for all forms of learning and memory. Repeated experiences of reward (for example, porn viewing) become associated with the stimuli in the user’s environment that precede them.
Interestingly, after repeated exposure to the same reward (in this example, porn), dopamine cells tend to fire more strongly in anticipation of viewing rather than in conjunction with actual viewing – although internet porn’s endless novelty means that using and anticipation are interwoven, in contrast with, say, a cocaine habit. As any addiction develops, cues and triggers, such as hearing a porn star’s name, time alone, or a mental state associated with past use (boredom, rejection, fatigue, etc.) can elicit conditioned, sudden surges of dopamine release. These surges then trigger cravings to use or even binge. Such conditioned responses may become deeply ingrained and can bring on strong cravings even long after someone quits using porn.
Although dopamine is sometimes thought of as a "pleasure molecule," this is technically inaccurate. Dopamine drives seeking and searching for reward – the anticipation, the wanting. In some unfortunate people, this seeking deepens into the disorder known as addiction. The user’s desperate search for satiety (that eventually often proves fleeting or unattainable) progresses to the point of marked distress or significant impairment in personal, family, social, educational, occupational, or other important areas of functioning.
However, addiction is now being defined not solely by this behavioral definition. It is also increasingly defined as a form of disordered reward learning. As Kauer and Malenka said, “addiction represents a pathological but powerful form of learning and memory.” This is why the American Society of Addiction Medicine (ASAM) redefined addiction as including both substances and behaviors. ASAM’s position is a recognition of the brain’s central role in driving what Marc Lewis called a “rut, a line of footprints in the neural flesh, which harden and become indelible.” (Lewis, Memoirs of an Addicted Brain, 2011).
ERROR #2 - “At a brain level sexual activity is no different from playing with puppies”
While playing with puppies might activate the reward system (unless you are a cat person), such activation doesn’t support the claim that all natural rewards are neurological equivalents. First, sexual arousal and orgasm induce far higher levels of dopamine and endogenous opioids than any other natural reward. Rat studies reveal that the dopamine levels occurring with sexual arousal equal those induced by the administration of morphine or nicotine.
Sexual arousal is also unique because it activates precisely the same reward system nerve cells as do addictive drugs. In contrast, there's only a small percentage of nerve-cell activation overlap between addictive drugs and natural rewards such as food or water. Not surprisingly, researchers have also established that the natural reward of food does not cause the same persistent change in synaptic plasticity as sexual activity (Chen et al., 2008).
However, this is not to say that gustatory reward cannot become addictive or disruptive to individuals and precipitate public health concerns, or cause brain changes in reward circuits. Any physician knows that obesity is a tremendous health concern consuming billions in medical costs, and dopamine receptor depletion in the brain’s reward center returns to more normal density with weight loss after gastric banding surgery. Also, the DNA transcripts which produce reward system proteins important in the craving states that are evoked with salt depletion/repletion are identical to those produced with drug craving (Leidke et al., 2011, PNAS). A National Geographic article on this paper said drugs “hijack” these natural reward pathways, and this is true for all addiction, whether to poker, porn, or popcorn.
Addictive drugs not only hijack the precise nerve cells activated during sexual arousal, they co-opt the same learning mechanisms that evolved to make us desire sexual activity. Activation of the same nerve cells that make sexual arousal so compelling helps explain why meth, cocaine, and heroin can be so addictive. Also, both sex and drug use can induce transcription factor DeltaFosB, resulting in neuroplastic alterations that are nearly identical for both sexual conditioning and chronic use of drugs.
While far too complex to elucidate in detail, multiple temporary neurological and hormonal changes occur with orgasm that do not occur with any other natural rewards. These include decreased brain androgen receptors, increased estrogen receptors, increased hypothalamic enkephalins, and increased prolactin. For example, ejaculation mimics the effects of chronic heroin administration on reward system nerve cells (the ventral tegmental area, or VTA). Specifically, ejaculation temporarily shrinks the same dopamine producing nerve cells that shrink with chronic heroin use, leading to temporary down-regulation of dopamine in the reward center (nucleus accumbens).
A 2000 fMRI study compared brain activation using two different natural rewards, one of which was porn. Cocaine addicts and healthy controls viewed films of: 1) explicit sexual content, 2) outdoor nature scenes, and 3) individuals smoking crack cocaine. The results: cocaine addicts had nearly identical brain activation patterns when viewing porn and viewing cues related to their addiction. (Incidentally, both cocaine addicts and healthy controls had the same brain activation patterns for porn.) However, for both the addicts and controls, brain activation patterns when viewing nature scenes were completely different from the patterns when viewing for porn. In short, there are multiple biological reasons we experience an orgasm differently from playing with puppies or viewing sunsets. Millions of adolescent boys and increasingly girls are not just watching puppies on the Internet, and Mindgeek knows that to make billions in ad revenues you name a site “Pornhub,” not “PuppyHub!”
ERROR #3 - “The brain effects of today’s porn are no different than static porn of the past”
This claim implies that all porn is equally harmless. However, as the recent paper Park et al., 2016 points out, research demonstrates that video porn is significantly more sexually arousing than other forms of porn. (I know of no research on VR porn yet.) In addition, the ability to self-select material makes internet porn more arousing than pre-selected collections. Today’s porn user can also maintain or heighten sexual arousal by clicking to a novel scene, new video or fresh genre. Novel sexual visuals trigger greater arousal, faster ejaculation, and more semen and erection activity than familiar material.
Thus today’s digital porn, with its limitless novelty, potent delivery (hi-def video or virtual), and the ease with which the user can escalate to more extreme material, appears to constitute a “supranormal stimulus.” This phrase, coined by Nobel laureate Nikolaas Tinbergen, refers to an exaggerated imitation of a stimulus that a species has evolved to pursue due to its evolutionary salience, but which can evoke more of a neurochemical response (dopamine) than the stimulus it imitates.
Tinbergen originally found that birds, butterflies, and other animals could be duped into preferring artificial substitutes designed specifically to appear more attractive than the animal's normal eggs and mates. Just as Tinbergen's and Magnus's ‘butterfly porn’ successfully competed for male attention at the expense of real females (Magnus, 1958; Tinbergen, 1951), so today’s porn is unique in its power to compete for users’ attention at the expense of real partners.
The three errors discussed above are typical of commentators anxious to ignore the brain’s central role in human volition, behavior, and emotion. One sexologist wrote, “There is brain science and neuroscience, but none of that applies to sexual science.” On the contrary, those educated in biology will increasingly understand the brain’s central role in every human activity. After all, both sexologists and neuroscientists alike should understand that the genitals take their marching orders from the brain, the primary sex organ.
Donald L. Hilton Jr, MD, FACS, FAANS is an adjunct associate professor of neurosurgery at the University of Texas Health Science Center at San Antonio, the director of the spine fellowship and the director of neurosurgical training at the Methodist Hospital rotation. He has authored numerous articles and speaks nationally and internationally on the neurobiology of porn use.
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