Decreased LPP for sexual images in problematic pornography users may be consistent with addiction models. Everything depends on the model (Commentary on Prause, Steele, Staley, Sabatinelli, & Hajcak, 2015)

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Biol Psychol. 2016 May 24. pii: S0301-0511(16)30182-X. doi: 10.1016/j.biopsycho.2016.05.003.

  • 1Swartz Center for Computational Neuroscience, Institute for Neural Computations, University of California San Diego, San Diego, USA; Institute of Psychology, Polish Academy of Science, Warsaw, Poland. Electronic address: mgola@ucsd.edu.

Internet technology provides affordable and anonymous access to a wide range of pornography content (Cooper, 1998). Avail-able data show that 67.6% of male and 18.3% of female Danish young adults (18–30 years old) use pornography on the regular weekly basis (Hald, 2006). Among USA college students 93.2% of boys and 62.1% of girls were watching online pornography before age of 18 (Sabina, Wolak, & Finkelhor, 2008). For the majority of users, pornography viewing plays a role in entertainment, excitement, and inspiration (Rothman, Kaczmarsky, Burke, Jansen, & Baughman, 2014) (Häggström-Nordin, Tydén, Hanson,& Larsson, 2009), but for some, frequent pornography consumption is a source of suffering (about 8% out of users according to Cooper et al., 1999) and becomes a reason for seeking treatment (Delmonico and Carnes, 1999; Kraus, Potenza, Martino, & Grant,2015; Gola, Lewczuk, & Skorko, 2016; Gola and Potenza, 2016). Due to its widespread popularity and conflicting clinical observations, pornography consumption is an important social issue, garnering much attention in the media, (e.g., high-profile movies: “Shame” by McQueen and “Don Jon” by Gordon-Levitt) and from politicians(e.g., UK prime minister David Cameron’s 2013 speech on pornography use by kids), as well as neuroscience research (Steele, Staley,Fong, & Prause, 2013; Kühn and Gallinat, 2014; Voon et al., 2014).One of the most frequently asked questions is: whether pornography consumption can be addicting?

The finding of Prause, Steele, Staley, Sabatinelli, & Hajcak, (2015) published in the June issue of Biological Psychology delivers interesting data on this topic. The researchers showed that men and women reporting problematic pornography viewing (N = 55),1 exhibited lower late positive potential (LPP – an event related potential in EEG signaling associated with significance and subjective silence of the stimuli) to sexual images as compared with non-sexual images, when compared with the responses of controls. They also show that problematic pornography users with higher sexual desire have smaller LPP differences for sexual and non-sexual images. The authors concluded that: “This pattern of results appears inconsistent with some predictions made by addiction models” (p. 196) and announced this conclusion in the article’s title: “Modulation of late positive potentials by sexual images in problem users and controls inconsistent with “porn addiction””.

Unfortunately, in their article, Prause et al. (2015) did not explicitly define which model of addiction they were testing. Presented results when considered in relation to the most established models either do not provide clear verification of the hypothesis that problematic pornography use is an addiction (like in case of Incentive Salience Theory; Robinson and Berridge, 1993; Robinson, Fischer, Ahuja, Lesser, & Maniates, 2015) or support this hypothesis (like in case of Reward Deficiency Syndrome; Blum et al., 1996; 1996; Blum, Badgaiyan, & Gold, 2015). Below I explain it in details.

Correspondence address: Swartz Center for Computational Neuroscience, Institute for Neural Computations, University of California San Diego, 9500 Gilman Drive, San Diego, CA 92093-0559, USA. E-mail address: mgola@ucsd.edu

1 It is worthy to notice that the authors present results for male and female participants together, while recent studies shows that sexual images ratings of arousal and valence differs dramatically between genders (see: Wierzba et al., 2015)

2 This guess is supported by fact that references used in Prause et al. (2015) also refer to IST (i.e. Wölfling et al., 2011

Why theoretical framework and clear hypothesis matter

Based on the multiple uses of the term “cue-reactivity” by the authors we may guess that the authors have in mind Incentive Salience Theory (IST) proposed by Robinson and Berridge (Berridge, 2012; Robinson et al., 2015).2 This theoretical frame-work distinguishes two basic components of motivated behavior − “wanting” and “liking”. The latter is directly linked to the experienced value of the reward, while the former is related to the expected value of the reward, typically measured in relation to a predictive cue. In terms of Pavlovian learning, reward is an unconditioned stimulus (UCS) and cues associated with this reward through learning are conditioned stimuli (CS). Learned CSs acquire incentive salience and evoke “wanting”, reflected in motivated behavior (Mahler and Berridge, 2009; Robinson & Berridge, 2013). Thus they acquire similar properties as the reward itself. For example domesticated quail willingly copulate with a terrycloth object (CS) previously paired with the opportunity to copulate with a female quail (UCS), even if a real female is available (Cetinkaya and Domjan, 2006)

According to IST, addiction is characterized by increased “wanting” (elevated cue-related reactivity; i.e. higher LPP) and decreased “liking” (diminished reward-related reactivity; i.e. lower LPP). In order to interpret data within the IST framework researchers must clearly disentangle cue-related “wanting” and reward-related “liking.” Experimental paradigms testing both processes introduce separate cues and rewards (i.e. Flagel et al., 2011; Sescousse, Barbalat, Domenech, & Dreher, 2013; Gola, Miyakoshi, & Sescousse, 2015). Prause et al. (2015) instead use a much simpler experimental paradigm, wherein subjects passively view different pictures with sexual and non-sexual content. In such simple experimental design the crucial question from the IST perspective is: Do the sexual images play the role of cues (CS) or rewards (UCS)? And therefore: does the measured LPP reflect “wanting” or “liking”?

The authors assume that sexual images are cues, and there-fore interpret decreased LPP as a measure of diminished “wanting.”Diminished “wanting” with respect to cues would indeed be inconsistent with the IST addiction model. But many studies show that sexual pictures are not mere cues. They are rewarding in them-selves (Oei, Rombouts, Soeter, van Gerven, & Both, 2012; Stoléru,Fonteille, Cornélis, Joyal, & Moulier, 2012; reviewed in: Sescousse,Caldú, Segura, & Dreher, 2013; Stoléru et al., 2012). Viewing sexual images evokes ventral striatum (reward system) activity (Arnowet al., 2002; Demos, Heatherton, & Kelley, 2012; Sabatinelli, Bradley,Lang, Costa, & Versace, 2007; Stark et al., 2005; Wehrum-Osinskyet al., 2014), dopamine release (Meston and McCall, 2005) and both self-reported and objectively measured sexual arousal (review: Chivers, Seto, Lalumière, Laan, & Grimbos, 2010).

The rewarding properties of sexual images may be innate due to the fact that sex (like food) is a primary reward. But even if some-one rejects such innate rewarding nature, rewarding properties of erotic stimuli may be acquired due to Pavlovian learning. Under natural conditions, visual erotic stimuli (such as a naked spouse or pornographic video) may be a cue (CS) for sexual activity leading to the climax experience (UCS) as a result of either dyadic sex or solitary masturbation accompanying pornography consumption. Furthermore in the case of frequent pornography consumption, visual sexual stimuli (CS) are strongly associated with orgasm (UCS) and may acquire properties of reward (UCS; Mahler and Berridge, 2009; Robinson & Berridge, 2013) and then lead to approach (i.e.seeking pornography) and consummatory behaviors (i.e., hours of viewing before reaching climax).

Regardless of innate or learned reward value, studies show that sexual images are motivating in themselves, even without the possibility of climax. Thus they have intrinsic hedonic value for humans (Prévost, Pessiglione, Météreau, Cléry-Melin, & Dreher,2010) as well as rhesus macaques (Deaner, Khera, & Platt, 2005).Their rewarding value may even be amplified in an experimental setting, where a climax experience (natural UCS) is unavailable, as in the Prause et al.’s (2015) study (“participants in this study were instructed not to masturbate during the task”, p. 197). According to Berridge, task context influences reward prediction (Berridge,2012). Thus, as no other pleasure than sexual images was available here, the viewing of pictures was the ultimate reward (rather than simply a cue).

Decreased LPP for sexual rewards in problematic pornography users is consistent with addiction models

Taking all of the above into account we may assume that sexual images in the Prause et al. (2015) study, instead of being cues, might have played the role of rewards. If so, according to the IST framework, lower LPP for sexual vs. non-sexual pictures in problematic pornography users and subjects with high sexual desire indeed reflects diminished “liking”. Such a result is in line with the addiction model proposed by Berridge and Robinson (Berridge, 2012; Robinson et al., 2015). However, to fully verify an addiction hypothesis within IST framework, more advanced experimental studies, disentangling cue and reward are required. A good example of a well designed experimental paradigm was used in studies on gamblers by Sescousse, Redouté, & Dreher (2010). It employed monetary and sexual cues (symbolic stimuli) and clear rewards (monetary wins or sexual pictures). Due to lack of well defined cues and rewards in Prause et al. (2015) study, role of sexual pictures remains unclear and therefore obtained LPP effects are ambiguous within IST framework. For sure conclusion presented in the study’s title “Modulation of late positive potentials by sexual images in problem users and controls inconsistent with “porn addiction” is ungrounded with respect to IST

If we take another popular addiction model – Reward Deficency Syndrome (RDS; Blum et al., 1996, 2015) the data obtained by the authors actually speaks in favor of addiction hypothesis. RDS frame-work assumes that genetic predisposition to lower dopaminergic response for rewarding stimuli (expressed in diminished BOLD and electrophysiological reactivity) is related to sensation-seeking, impulsivity and higher risk of addiction. The authors’ findings of lower LPPs in problematic pornography users is entirely consistent with the RDS addiction model. If Prause et al. (2015) were testing some other model, less well known than IST or RDS, it would be highly desirable to present it briefly in their work.

Final remarks

The study by Prause et al. (2015) delivers interesting data on problematic pornography consumption.3 Yet, due to the lack of clear hypothesis statement which addiction model is tested and ambiguous experimental paradigm (hard to define role of erotic pictures), it is not possible to say if the presented results are against, or in favor of, a hypothesis about “pornography addiction.” More advanced studies with well defined hypotheses are called for. Unfortunately the bold title of Prause et al. (2015) article has already had an impact on mass media,4 thus popularizing scientifically unjustified conclusion. Due to the social and political importance of the topic of the effects of pornography consumption, researchers should draw future conclusions with greater caution.

3 It is worthy to notice that in Prause et al. (2015) problematic users consume pornography in average for 3.8 h/week (SD = 1.3) it is almost the same as non-problematic pornography users in Kühn and Gallinat (2014) who consume in average 4.09 h/week (SD = 3.9). In Voon et al. (2014) problematic users reported 1.75 h/week (SD = 3.36) and problematic 13.21 h/week (SD = 9.85) – data presented by Voon during American Psychological Science conference in May 2015.

4 Examples of titles of popular science articles about Prause et al. (2015):“Porn is not as harmful as other addictions, study claims” (http://metro.co.uk/2015/07/04/porn-is-not-as-harmful-as-other-addictions...), “Your Porn Addiction Isn’t Real” (http://www.thedailybeast.com/articles/2015/06/26/your-porn-addiction-isn...), “Porn ’Addiction’ Isn’t Really Addiction, Neuroscientists Say” (http://www.huffingtonpost.com/2015/06/30/porn-addiction- n7696448.html)

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