This research summary was co-authored by Lisa Thompson (Vice President and Director of the NCOSE Research Institute) and Jordan Marshall (Research Assistant).
Have you ever wondered why people with substance abuse disorders or behavioral addictions persist in their destructive behavior despite all the negative consequences?
You aren’t alone.
Scientists have long been seeking the answer to this same question. As it turns out, a couple of them developed an important theory that provides a likely answer.
Incentive Sensitization Theory Explained
Incentive Sensitization Theory (IST), a prominent model of addiction, explores the role of motivation and neurobiology in reward-related behavior.[1] Developed by Drs. Terry Robinson and Kent Berridge, the theory holds that under certain circumstances repeated exposure to potentially addictive rewards causes changes to the brain cells and systems that normally regulate our motivation to seek rewards (e.g., a pleasure inducing drug).
Based on findings from their scientific experiments, they argued that repeated exposure to drug rewards results in “neuroadaptations” in the brain that make it “sensitized” to cues associated with reward, potentially to a pathological degree.[2] In the context of drug addiction, this means that cues associated with drug use (any of numerous sights, sounds, smells, or tastes) that our brains associate with a “rewarding” drug can take on extreme importance and drive a person’s behavior to seek the reward despite adverse outcomes.
Since it was first proposed in 1993, IST has been used to probe a wide range of possible substance and behavioral addictions including alcohol, nicotine, smoking, gambling, eating disorders, video gaming, and importantly for us[3]—compulsive pornography use.[4]
Rewards and the Reward System
Rewards and the brain’s reward system are important elements to understanding IST. Rewards are environmental stimuli including objects, events, and activities that motivate organisms to approach and consume or engage in them.[5] Rewards are things we see, feel, taste, smell, or hear.[6] They are attractive and have the potential to produce learning as well as to create feelings of pleasure.[7] Primary rewards are those necessary for individual survival such as food and liquid, as well as survival of the species—sex.[8] On the other hand, are nonprimary rewards which can be physical (a fancy car) or nonphysical (novelty and gambling).[9] Importantly, the assessment of a reward’s value is determined by brain activity which evaluates the potential of a reward to sustain life, as well as the level of pleasure associated with the reward. This activity is carried out by the brain’s reward system.[10] To learn more about how the brain’s reward system works click here and here.
“Liking” vs. “Wanting”
IST has identified two separate but interconnected neural systems in the brain which are responsible for spurring us to seek rewards: 1) the hedonic or “liking”[11] system and 2) the motivational system, which is referred to as incentive salience or more simply “wanting”—a visceral feeling of desire.[12] IST maintains that “While we typically want the things that we like and like the things that we want” these two experiences are not synonymous and the processes, which normally work in tandem, can become dissociated.[13] A key player in how the process of dissociation occurs is the neurotransmitter[14] dopamine. We will explore the role of dopamine in IST shortly.
“Liking” (i.e., Hedonic Pleasure)
Among humans liking is generally thought of as our conscious, subjective response to pleasurable stimuli.[15] In IST, however, “liking” does not refer to a conscious process, but rather to affective reactions that are not experienced subjectively.[16] For instance, orofacial expressions such as lip licking and rhythmic tongue protrusions are behavioral expressions of “liking” that can occur in the absence of conscious liking and have been used as measures of “liking” in experiments involving rats, apes, and humans.[17] Also noteworthy, “liking” occurs during or immediately after reward consumption or consummation.[18]
It was once believed that dopamine was the neurotransmitter largely responsible for our sensations of pleasure,[19] but research has surprisingly revealed that “liking” is not a dopamine-dependent phenomenon.[20] For instance, in laboratory experiments in which some rats were depleted of dopamine and others were not, the dopamine-depleted rats still exhibited pleasurable reactions to a sweet liquid to the same extent as control rats.[21]
Rather than being responsible for pleasure, research has revealed that dopamine’s role lies in its ability to encode prediction of reward, imprint “incentive” value to reward cues, and facilitate learning of reward associations.[22] In short, it is now believed that dopamine plays a central role in motivating us to seek rewards,[23] which brings us to “wanting.”
“Wanting” (i.e., Incentive Salience)
“Wanting”—in contrast to “liking”—is a dopamine-dependent process which occurs before the reward.[24] Reward-related substances and activities such as eating a piece of chocolate cake, experiencing a drug high, or having a win at the slot machines stimulate dopamine transmission in the brain.[25] While dopamine cells fire when first exposed to a novel reward, “repeated exposure to DA [dopamine] causes the neurons to stop firing upon reward consumption and to fire instead when they are exposed to stimuli that are predictive of the reward.”[26]
Over time, the repeated use of or engagement in a reward can produce changes to the brain’s mesolimbic dopamine system[27] making the brain increasingly sensitized or conditioned to cues (e.g., the smell of chocolate, places or friends associated with drug use, or the sight of money, etc.[28]) that are associated with the reward. These cues become attention-grabbing and riveting, and act as motivating triggers to obtain and consume the reward again.[29] Thus, incentive salience is the component of the reward process through which unconscious perceptions of cues or stimuli become salient—that is made attractive, desired, or wanted.[30] Also of importance, “wanting” differs from cognitive or “explicit” desires which are based on high-level, goal-related systems in the brain that rely on past memories of liking experiences.[31]
Role of Dopamine in “Wanting”
Though not the only neurotransmitter involved in mesolimbic sensitization, dopamine plays a central role in “wanting.” Early sensitization research focused on increases in the release of dopamine, finding that “a sensitized dopamine system . . . is hyperreactive to drug cues and contexts,” resulting in heightened dopamine release and brain activations.[32] For instance, studies have confirmed that drug cues trigger higher increases in dopamine release and “the greater the cue-induced dopamine release the greater the craving” for more drugs.[33]
When dopamine is released into the space between neurons, it binds to dopamine receptors to “turn on” the target cells in the reward area.[34] Excessive dopamine release over time can make dopamine receptors less receptive or suppressed, a process called downgrading or downregulation.[35] This means greater stimulation will be required to “turn on” these cells.[36] This downgrading of dopamine receptors can result in tolerance to drug effects leading addicts to take higher doses of a drug in order to get high,[37] or in the case of pornography users, may lead them to seek more extreme pornography.[38] Other neurotransmitters and neurons may be changed by sensitization as well, but the fact remains that sensitization of brain dopamine systems make “brain ‘wanting’ systems hyperreactive to drug cues and contexts” and once sensitization occurs the effects are “very long lasting, and possibly even permanent.”[39]
IST and Classical Conditioning
It would be easy to assume that incentive-salience (e.g., “wanting”) is simply the process of associative learning known as classical or Pavlovian conditioning (for more background on classical conditioning see this article). However, incentive salience is a specific form of Pavlovian conditioning, which through the neurobiological state of mesolimbic circuits, translates mere knowledge about reward into actual motivation to seek it.[40]
Sensitization
As noted earlier, excessive levels of sensitization to cues are manifested as intense “wanting” or craving—a known feature of addiction.[41] Ultimately, people can become so reactive to reward cues that cues “become powerful enough to direct and sometimes dictate behavior.”[42] Thus, IST predicts and provides a likely explanation for the well-known “pathological and compulsive pattern of drug-seeking and drug-taking behaviors, which occupies an inordinate amount of an individual’s time and thoughts, and persists despite adverse consequences,”[43] as well as for other substances and behaviors.
Dissociation between “Liking” and “Wanting”
Importantly, studies of substance,[44] gambling disorders,[45] and compulsive pornography use [46] have all demonstrated this dissociation between “wanting” and “liking” (sometimes referred to as the “paradox of addiction”[47]). While cravings increase in response to reward cues, the actual pleasure or “liking” derived from the reward decreases.[48]
This irrational “wanting”—the desire for that which is not expected or remembered as liked, as well as not actually liked when obtained—is often evoked by learned cues associated with reward.[49] Though potentially addictive substances and behaviors initially produce feelings of pleasure, these feelings of pleasure or “liking” can decrease over time with repeated use.[50]cThe dissociation between wanting and liking explains why people with addictions continue use of addictive substances or engage in certain behaviors despite decreased pleasure and negative consequences. As Berridge and Robinson explain, the “sensitized ‘wanting’ can persist for years, even if the person cognitively does not want to take drugs, does not expect the drugs to be very pleasant, and even long after withdrawal symptoms have subsided.”[51]
There is Hope for Recovery
For anyone who has had the tragic experience of suffering from addiction or had a loved one succumb to an addiction of any type, as this review of IST theory reveals, science is shining light on why many people persist in their addiction despite the often catastrophic consequences. Research shows that the process of addiction leads to neurobiological changes in the brain’s function that creates a self-reinforcing feedback loop which can urge people to seek rewards long after the pleasure associated with the reward has ceased. Imminent addiction scholars have summed it up well: “The last 25 years of neuroscience research have produced evidence that addiction is a disease of the brain. . . .”[52]
To learn more about how research on compulsive pornography use is lining up with IST visit yourbrainonporn.com.
Addictions can be very difficult to overcome, but as many people can attest, recovery is possible with the right resources and support. If you or someone you know is struggling with pornography addiction, or you’ve been hurt by someone else’s addiction, here are several resources where you can learn more and/or find community support.
International Institute for Trauma and Addiction Professionals
References
[1] Terry E. Robinson and Kent C. Berridge, “The Incentive Sensitization Theory of Addiction: Some Current Issues,” Philosophical Transactions of the Royal Society of London, Series B, Biological Sciences 363 (2008): 3137–3146, doi:10.1098/rstb.2008.0093; Terry E. Robinson and Kent C. Berridge, “The Neural Basis of Drug Craving: An Incentive-Sensitization Theory of Addiction,” Brain Research Review 18 (1993): 247‒291.
[2] Robinson and Berridge, “Some Current Issues,” ibid.
[3] Eva Pool et al., “Measuring Wanting and Liking from Animals to Human: A Systematic Review,” Neuroscience and Biobehavioral Reviews 63 (2016): 124–142
[4] Mateusz Gola et al., “Can Pornography be Addictive? An fMRI Study of Men Seeking Treatment for Problematic Pornography Use,” Neuropsychopharmacology 42 (2017): 2021–2031.
[5] Wolfram Schultz, “Neuronal Reward and Decision Signals: From Theories to Data,” Physiological Reviews 95, no. 3 (2015): 853–951, doi:10.1152/physrev.00023.2014.
[6] Ibid.
[7] Ibid.
[8] Ibid
[9] Ibid.
[10] The brain’s reward system consists of circuitry that links the ventral tegmental area, nucleus accumbens, and ventral pallidum via the medial forebrain bundle. These circuits are also believed to encode attention, expectancy of reward, disconfirmation of reward expectancy, and incentive motivation. See: Eliot L. Gardner, “Introduction: Addiction and Brain Reward and Anti-Reward Pathways,” Advances in Psychosomatic Medicine 30 (2011): 22-60, doi:10.1159/000324065.
[11] Hedonic “liking” is not to be confused with “expected pleasantness,” which involves cognitive processes that predict one’s expectations of how pleasant a reward will be and are a function of goal-oriented behavior rather than the distinct motivational control system. Please note: quotations marks are being used to differentiate subconscious “liking” and “wanting” from conscious liking and wanting.
[12] M.J.F. Robinson et al., “Roles of ‘Wanting’ and ‘Liking’ in Motivating Behavior: Gambling, Food, and Drug Addictions,” Behavioral Neuroscience of Motivation 27 (2016): 105–136.
[13] Ibid, 106; see also Kent C. Berridge and Terry E. Robinson, “Parsing Reward,” Trends in Neuroscience 26, no. 9 (2003): 507–513.
[14] Neurotransmitters are chemical signals allowing communication between neurons in the brain. See: Thomas C. Süudhof, “Neurotransmitter Release,” in Pharmacology of Neurotransmitter Release, Handbook of Experimental Pharmacology, vol. 184, eds. Thomas C. Süudhof and Klaus Starke, (Berlin, Heidelberg: Springer, 2008), 1-21, doi:10.1007/978-3-540-74805-2.
[15] Robinson et al., “Roles of ‘Wanting’ and ‘Liking,’” ibid.
[16] Berridge and Robinson, “Parsing Reward,” ibid.
[17] Robinson et al., “Roles of ‘Wanting’ and ‘Liking,’” ibid.
[18] Pool et al., ibid.
[19] Berridge and Robinson, “Parsing Reward,” ibid.
[20] Robinson et al., “Roles of ‘Wanting’ and ‘Liking,’” ibid.
[21] Kent C. Berridge and Terry E. Robinson, “What Is the Role of Dopamine in Reward: Hedonic Impact, Reward Learning, or Incentive Salience?” Brain Research Reviews 28, (1998): 309–369.
[22] N.D. Volkow and R.D. Baler, “Addiction Science: Uncovering Neurobiological Complexity,” Neuropharmacology 76 (2014): 238, doi:10.1016/j.neuropharm.2013.05.007.
[23] Berridge and Robinson, “Parsing Reward,” ibid.
[24] Pool et al., ibid.
[25] Kenneth Blum et al., “The Addictive Brain: All Roads Lead to Dopamine,” Journal of Psychoactive Drugs 44, no. 2 (2012): 134–143.
[26] Volkow and Baler, ibid, 241.
[27] Associated with the central part of the limbic system, the mesolimbic dopamine pathway consists of neural networks connecting the ventral tegmental area of the brain to the nucleus accumbens. See: Donald L. Hilton Jr., Stephanie Carnes, and Todd L. Love, “The Neurobiology of Behavioral Addictions,” in Neurobiology of Addiction, eds. Alan C. Swann, F. Gerard Moeller, and Marijn Lijffijt(New York, NY: Oxford University Press, 2016).
[28] Paula Banca et al., “Novelty, Conditioning and Attentional Bias to Sexual Rewards,” Journal of Psychiatric Research 72 (2016): 92, doi:10.1016/j.jpsychires.2015.10.017.
[29] Berridge and Robinson, “Parsing Reward,” ibid.
[30] Pool et al., ibid; Berridge and Robinson, “Parsing Reward,” ibid.
[31] Pool et al., ibid.
[32] Kent C. Berridge and Terry E. Robinson, “Liking, Wanting, and the Incentive-Sensitization Theory of Addiction,” American Psychologist 71, no. 8 (2016): 673, doi:10.1037/amp0000059.
[33] Marco Leyton and Paul Vezina, “Striatal Ups and Downs: Their Roles in Vulnerability to Addictions in Humans,” Neuroscience & Biobehavioral Reviews 37, no. 9 (2013): 2004, doi:10.1016/j.neubiorev.2013.01.018.
[34] Dr. Don Hilton, email messages to author, September 27-28, 2021.
[35] Ibid.
[36] Ibid.
[37] Berridge and Robinson, “Liking, Wanting,” ibid.
[38] Simone Kühn and Jürgen Gallinat, “Brain Structure and Functional Connectivity Associated with Pornography Consumption: The Brain on Porn,” JAMA Psychiatry 71, no. 7 (2014): 827-834, doi:10.1001/jamapsychiatry.2014.93
[39] Berridge and Robinson, “Liking, Wanting,” ibid, 673.
[40] Kent C. Berridge, “From Prediction Error to Incentive Salience: Mesolimibic Computation of Reward Motivation,” European Journal of Neuroscience 35 (2012): 1124–1143, doi: 10.1111/j.1460-9568.2012.07990.x.
[41] Simone Kühn and Jürgen Gallinat, “Common Biology of Craving across Legal and Illegal Drugs – a Quantitative Meta-Analysis of Cue-Reactivity Brain Response,” European Journal of Neuroscience 33 (2011): 1318-1326, doi:10.1111/j.1460-9568.2010.07590.x.
[42] Robinson et al., “Roles of ‘Wanting’ and ‘Liking,’” ibid, 108.
[43] Robinson and Berridge, “Some Current Issues,” ibid, 3137.
[44] Laura Anne Grigutsch et al., “Implicit ‘Wanting’ Without Implicit ‘Liking’: A Test of Incentive-Sensitization-Theory in the Context of Smoking Addiction using the Wanting-Implicit-Association-Test (W-IAT),” Journal of Behavior Therapy and Experimental Psychiatry 64 (2019): 9-14, doi:10.1016/j.jbtep.2019.01.002; Robinson et al., “Roles of ‘Wanting’ and ‘Liking,’” ibid.
[45] Kristine Rømer Thomsen et al., “Applying Incentive Sensitization Models to Behavioral Addiction,” Neuroscience and Biobehavioral Reviews 45 (2014): 343–349, doi.org/10.1016/j.neubiorev.2014.07.009; Klaus Wölfing et al., “To Gamble or Not to Gamble: At Risk for Craving and Relapse – Learned Motivated Attention in Pathological Gambling,” Biological Psychology 87 (2011): 275–281; Belinda Davey and Robert Cummins, “Testing an Incentive-Sensitisation Approach to Understanding Problem Slot-Machine Gambling Using an Online Slot-Machine Simulation,” Journal of Gambling Studies 34 (2018): 773-784, doi:10.1007/s10899-017-9718-y; Samantha N. Hellberg, Trinity I. Russell, and Mike J.F. Robinson, “Cued for Risk: Evidence for an Incentive Sensitization Framework to Explain the Interplay between Stress and Anxiety, Substance Abuse, and Reward Uncertainty in Disordered Gambling Behavior,” Cognitive, Affective, & Behavioral Neuroscience 19 (2019): 737-758, doi:0.3758/s13415-018-00662-3.
[46] Gola et al., ibid.
[47] Grigutsch et al., ibid.
[48] This is possible since, as noted earlier, there are two distinct brain systems controlling “wanting” verses “liking.”
[49] Berridge, “Prediction Error to Incentive Salience,” ibid.
[50] Robinson and Berridge, “Some Current Issues,” ibid, 3142.
[51] Berridge and Robinson, “Liking, Wanting,” ibid, 673.
[52] Nora D. Volkow et al., “Addiction: Decreased Reward Sensitivity and Increased Expectation Sensitivity Conspire to Overwhelm the Brain’s Control Circuit,” Bioessays 32, no. 9 (2010): 748–755, doi:10:1002/bies.201000042.
