Donald L. Hilton, Jr. MD, FACS
Clinical Associate Professor
Department of Neurosurgery
University of Texas Health Sciences Center at San Antonio
The human brain is programmed to incentivize behaviors that contribute to survival. The mesolimbic dopaminergic system rewards eating and sexuality with powerful pleasure incentives. Cocaine, opioids, alcohol, and other drugs subvert, or hijack, these pleasure systems, and cause the brain to think a drug high is necessary to survive. Evidence is now strong that natural rewards such as food and sex affect the reward systems in the same way drugs affect them, thus the current interest in ‘natural addiction.’ Addiction, whether to cocaine, food, or sex occurs when these activities cease to contribute to a state of homeostasis, and instead cause adverse consequences. For instance, when eating causes morbid obesity few will argue that the organism is in healthy balance. Similarly, pornography causes harm when it impairs or destroys a person’s ability to develop emotional intimacy.
A decade ago evidence began to point to the addictive nature of over-consumption of natural behaviors which cause a dopaminergic reward to be experienced in the brain. For instance, Dr. Howard Shaffer, Director of Addiction Research at Harvard University, said in 2001, “I had great difficulty with my own colleagues when I suggested that a lot of addiction is the result of experience … repetitive, high-emotion, high-frequency experience. But it’s become clear that neuroadaptation–that is, changes in neural circuitry that help perpetuate the behavior–occurs even in the absence of drug-taking” In the decade since he said this, he has focused his research more and more on the brain effects of natural addictions such as gambling. Note the following from this same Science paper from 2001
The experts are fond of saying that addiction occurs when a habit “hijacks” brain circuits that evolved to reward survival- enhancing behavior such as eating and sex. “It stands to reason if you can derange these circuits with pharmacology, you can do it with natural rewards too,” observes Stanford University psychologist Brian Knutson. Thus, drugs are no longer at the heart of the matter. “What is coming up fast as being the central core issue … is continued engagement in self-destructive behavior despite adverse consequences,” says Steven Grant of NIDA.
In the decade since these revolutionary concepts were first described, the evidence for the natural reward addiction concept has only strengthened. In 2005 Dr. Eric Nestler, now chairman of neuroscience at Mount Sinai Medical Center in New York published a landmark paper in Nature Neuroscience titled “Is There a Common Pathway for Addiction?” He said: ““Growing evidence indicates that the VTA-NAc pathway and the other limbic regions cited above similarly mediate, at least in part, the acute positive emotional effects of natural rewards, such as food, sex and social interactions. These same regions have also been implicated in the so-called ‘natural addictions’ (that is, compulsive consumption of natural rewards) such as pathological overeating, pathological gambling and sexual addictions. Preliminary findings suggest that shared pathways may be involved: [an example is] cross-sensitization that occurs between natural rewards and drugs of abuse.”
In 2002 a study on cocaine addiction was published which demonstrated measurable volume loss in several areas of the brain, including the frontal lobes. The technique was to use an MRI-based protocol called voxel-based morphometry (VBM), where one millimeter cubes of brain are quantified and compared. Another VBM study was published in 2004 on methamphetamine with very similar findings. While interesting, these findings are not surprising to either the scientist or the layperson, as these are “real drugs.”
The story does become more interesting when we look at a natural addiction such as overeating leading to obesity. In 2006 a VBM study was published looking specifically at obesity, and the results were very similar to the cocaine and methamphetamine studies. The obesity study demonstrated multiple areas of volume loss, particularly in the frontal lobes, areas associated with judgment and control. While this study is significant in demonstrating visible damage in a natural endogenous addiction, as opposed to an exogenous drug addiction, it is still easier to accept intuitively because we can see the effects of overeating in the obese person.
So what about sexual addiction? In 2007 a VBM study out of Germany looked specifically at pedophilia, and demonstrated almost identical finding to the cocaine, methamphetamine, and obesity studies. The significance of this study in relation to this discussion is most relevant in that It demonstrates that a sexual compulsion can cause physical, anatomic change in the brain, i.e., harm. Interestingly, a recent paper found a high correlation between pedophilic pornography and sexually abusing children. This noted, the paper thus focused on a subgroup with, among other problems, severe pornography addiction. While we may draw ethical and legal distinctions between child and adult pornography, the brain is not likely to have such an age-related set point with regard to dopaminergic downgrading and addiction-based volume loss. Does the brain care whether the person is physically experiencing sexuality, or doing it through the medium of object sex, i.e., pornography. The mirror systems of the brain turn the virtual experience of pornography into a real experience, as far as the brain is concerned. This is supported by a recent study from France showing activation of areas associated with mirror neurons in the human brain in males viewing pornography. The authors conclude, “we suggest that… the mirror-neuron system prompts the observers to resonate with the motivational state of other individuals appearing in visual depictions of sexual interactions.” A preliminary study supports frontal damage specifically in patients unable to control their sexual behavior. This study used diffusion MRI to evaluate function of nerve transmission through white matter, where the axons, or wires connecting nerve cells, are located. It demonstrated dysfunction in the superior frontal region, an area associated with compulsivity, a hallmark of addiction.
Numerous studies demonstrate metabolically pathologic changes in neurochemistry as the brain “learns” to become addicted. These addictive changes in the dopamine reward system can also be scanned with brain scans such a functional MRI, PET, and SPECT scans. While we would expect a brain scan study to show abnormalities in dopamine metabolism in cocaine addiction, we might be surprised to find that a recent study also shows dysfunction of these same pleasure centers with pathologic gambling. Overeating leading to obesity, another natural addiction, also shows similar pathology.
Also pertinent is a paper from the Mayo Clinic on treatment of Internet pornography addiction with naltrexone, an opioid receptor antagonist. Drs. Bostsick and Bucci at Mayo Clinic treated a patient with the inability to control his Internet pornography use.
He was placed on naltrexone, a drug which acts on the opioid system to decrease dopamine’s ablility to stimulate cells in the nucleus accumbens. With this drug he was able to obtain control of his sexual life.
The authors conclude:
In summary, cellular adaptations in the addict’s PFC result in increased salience of drug-associated stimuli, decreased salience of non-drug stimuli, and decreased interest in pursuing goal-directed activities central to survival. In addition to naltrexone’s approval from the Food and Drug Administration for treating alcoholism, several published case reports have demonstrated its potential for treating pathologic gambling, self-injury, kleptomania, and compulsive sexual behavior. We believe this is the first description of its use to combat Internet sexual addiction.
The prestigious Royal Society of London was founded in the 1660’s, and publishes the longest running scientific journal in the world. In a recent issue of the Philosophical Transactions of the Royal Society, the current state of the understanding of addiction was reported as it was discussed by some of the world’s leading addiction scientists at a meeting of the Society. The title of the journal issue reporting the meeting was “The neurobiology of addiction – new vistas.” Interestingly, of the 17 articles, two were specifically concerned with natural addiction: pathologic gambling and a paper by Dr. Nora Volkow on similarities in brain dysfunction in drug addiction and in overeating. A third paper by Dr. Nestler addressed animal models of natural addiction as well with regard to DFosB.
DFosB is a chemical which Dr. Nestler has studied, and appears to be found in the neurons of addicted subjects. It appears to have a physiologic role is well, but is strongly implicated in addiction Interestingly, it was first found in the brain cells of animals studied in drug addiction, but has now been found in brain cells in the nucleus accumbens related to over-consumption of natural rewards.[i] A recent paper investigating DFosB and its role in over-consumption of two natural rewards, eating and sexuality, concludes:
In summary, the work presented here provides evidence that, in addition to drugs of abuse, natural rewards induce DFosB levels in the Nac…our results raise the possibility that DFosB induction in the NAc may mediate not only key aspects of drug addiction, but also aspects of so-called natural addictions involving compulsive consumption of natural rewards.
Dr. Nora Volkow is head of the National Institute on Drug Abuse (NIDA), and is one of the most published and respected addiction scientists in the world. She has recognized this evolution in the understanding of natural addiction and advocated changing the name of the NIDA to the National Institute on Diseases of Addiction. The journal Science reports: “NIDA director Nora Volkow also felt that her institute’s name should encompassaddictions such as pornography, gambling, and food, says NIDA adviser Glen Hanson. ‘She would like to send the message that [we should] look at the whole field.’” (emphasis added).
In summary, in the last 10 years the evidence is now firmly supportive of the addictive nature of natural rewards. Drs. Malenka and Kauer, in their landmark paper on the mechanism of the chemical changes which occur in the brain cells of addicted individuals state, “addiction represents a pathological, yet powerful form of learning and memory.” We now call these changes in brain cells “long term potentiation” and “long term depression,” and speak of the brain as being plastic, or subject to change and re-wiring. Dr. Norman Doidge, a neurologist at Columbia, in his book The Brain That Changes Itself describes how pornography causes re-wiring of the neural circuits. He notes a study on men viewing Internet pornography in which they looked “uncannily” like rats pushing the lever to receive cocaine in the experimental Skinner boxes. Like the addicted rat, they are desperately seeking the next fix, clicking the mouse just as the rat pushes the lever. Pornography addiction is frantic learning, and perhaps this is why many who have struggled with multiple addictions report that it was the hardest addiction for them to overcome. Drug addictions, while powerful, are more passive in a “thinking” kind of way, whereas pornography viewing, especially on the Internet, is a much more active process neurologically. The constant searching and evaluating each image or video clip produced for potency and effect is an exercise in neuronal learning and rewiring.
Human sexual climax utilizes the same reward pathways as those mobilized during a heroin rush. If we fail to understand the implications of pornography’s ability to re-program the brain structurally, neurochemically, and metabolically, we doom ourselves to continue to fail in treating this formidable disease. However, if we accord this powerful natural reward the appropriate focus and emphasis we can help many now trapped in addiction and despair find peace and hope.
 Constance Holden, “Behavioral Addictions: Do They Exist? Science, 294 (5544) 2 November 2001, 980.
 Eric J. Nestler, “Is there a common molecular pathway for addiction?” Nature Neuroscience 9(11):1445-9, Nov 2005
 Teresa R. Franklin, Paul D. Acton, Joseph A Maldjian, Jason D. Gray, Jason R. Croft, Charles A. Dackis, Charles P. O’Brien, and Anna Rose Childress, “Decreased Gray Matter Concentration in the Insular, Orbitofrontal, Cingulate, and Temporal Cortices of Cocaine Patients,” Biological Psychiatry (51)2, January 15, 2002, 134-142.
 Paul M. Thompson, Kikralee M. Hayashi, Sara L. Simon, Jennifer A. Geaga, Michael S. Hong, Yihong Sui, Jessica Y. Lee, Arthur W. Toga, Walter Ling, and Edythe D. London, “Structural Abnormalities in the Brains of Human Subjects Who Use Methamphetamine,” The Journal of Neuroscience, 24(26) June 30 2004;6028-6036.
 Nicola Pannacciulli, Angelo Del Parigi, Kewei Chen, Dec Son N.T. Le, Eric M. Reiman and Pietro A. Tataranni, “Brain abnormalities in human obesity: A voxel-based morphometry study.” Neuroimage 31(4) July 15 2006, 1419-1425.
 Boris Schiffer, Thomas Peschel, Thomas Paul, Elke Gizewshi, Michael Forshing, Norbert Leygraf, Manfred Schedlowske, and Tillmann H.C. Krueger, “Structural Brain Abnormalities in the Frontostriatal System and Cerebellum in Pedophilia,” Journal of Psychiatric Research (41)9, November 2007, 754-762.
 M. Bourke, A. Hernandez, The ‘Butner Study’ Redux: A Report of the Incidence of Hands-on Child Victimization by Child Pornography Offenders. Journal of Family Violence 24(3) 2009, 183-191.
 H. Mouras, S. Stole4ru, V. Moulier, M Pelegrini-Issac, R. Rouxel, B Grandjean, D. Glutron, J Bittoun, Activation of mirror-neuron system by erotic video clips predicts degree of induced erection: an fMRI study. NeuroImage 42 (2008) 1142-1150.
 Michael H. Miner, Nancy Raymond, BryonA. Meuller, Martin Lloyd, Kelvin Ol Lim,“Preliminary investigation of the impulsive and neuroanatomical characteristics of compulsive sexual behavior.” Psychiatry Research Neuroimaging Volume 174, Issue 2, November 30 2009, Pages 146-151.
 Bruce E. Wexler, Christopher H. Gottschalk, Robert K. Fulbright, Isak Prohovnik, Cheryl M. Lacadie, Bruce J. Rounsaville, and John C. Gore, “Functional Magnetic Resonance Imaging of Cocaine Craving,” American Journal of Psychiatry, 158, 2001, 86-95.
 Jan Reuter, Thomas Raedler, Michael Rose, Iver Hand, Jan Glascher, and Christian Buchel, “Pathological gambling is linked to reduced activation of the mesolimbic reward system,” Nature Neuroscience 8, January 2005, 147-148.
 Gene-Jack Wang, Nora D. Volkow, Jean Logan, Naomi R. Pappas, Christopher T. Wong, Wei Zhu, Noelwah Netusil, Joanna S Fowler, “Brain dopamine and obesity,” Lancet 357(9253) February 3 2001, 354-357.
 J. Michael Bostwick and Jeffrey A. Bucci, “Internet Sex Addiction Treated With Naltrexone.” Mayo Clinic Proceedings, 2008, 83(2):226-230.
 Marc N. Potenza, “The neurobiology of pathologic gambling and drug addiction: an overview and new findings,” Philosophical Transactions of the Royal Society, 363, 2008, 3181-3190..
 Nora D. Volkow, Gene-Jack Wang, Joanna S. Fowler, Frank Telang, “Overlapping neuronal circuits in addiction and obesity: evidence of systems pathology,” Philosophical Transactions of the Royal Society, 363, 2008, 3191-3200.
 Eric J. Nestler, “Transcriptional mechanisms of addiction: role of DFosB,” Philosophical Transactions of the Royal Society, 363, 2008, 3245-3256.
 D.L. Wallace, et al, The Influence of DFosB in the Nucleus Accumberns on Natural reward-Related Behavior,The Journal of Neuroscience, 28(4): October 8, 2008, 10272-10277,
 Science 6 July 2007:?Vol. 317. no. 5834, p. 23
 Julie A. Kauer, Robert C. Malenka, “Synaptic Plasticity and Addiction,” Nature Reviews Neuroscience, 8, 8440858 November 2007, 844-858.
 Gert Holstege, Janniko R. Georgiadis, Anne M.J. Paans, Linda C. Meiners, Ferdinand H.C. E. van der Graaf, and A.A.T. Simone Reinders, “ Brain activation during human male ejaculation,” The Journal of Neuroscience 23 (27), 2003, 9185-9193