________________________________________________________________________ Behavioral Addictions
PATHOPHYSIOLOGY The bulk of recent neuroscience research in sexual addiction has studied addictive Internet pornography use and, unfortu- nately, almost exclusively involves male research participants. Nonetheless, this research has importantly clarified pathogenic and pathophysiologic processes, the marked similarities to sub- stance addictions, and the pathogenesis and pathophysiology of Internet pornography addiction, hypersexuality, and Internet pornography use-induced sexual dysfunction. The importance of this research is underscored by findings of a long-term study that Internet pornography may have the highest addiction potential of any online activity (with Internet gaming a close second) [158]. Cue reactivity, or the level of sexual arousal to Internet pornog- raphy, is the greatest single predictor of Internet pornography addiction, severity of the addiction, and impairment from the addiction. Hours of use alone is unrelated to addiction. Cue reactivity is an established correlate of addictive behavior across addiction disorders [151; 159]. Internet pornography addiction severity is directly related to cue-induced activation of the dorsolateral PFC and thalamus [151; 159]. Male sexual response is actually complex. One core mechanism is the hypothalamic nuclei, which regulates sexual behavior and erections by integrating brain and peripheral input. Pro- erectile input comes from mesolimbic dopamine pathways—the ventral tegmental area and the nucleus accumbens. The ventral tegmental area and nucleus accumbens form the core of a set of integrated circuits, termed the “reward system,” that detects reward stimuli and regulates response to sex and other rewards. The mesolimbic dopamine pathway receives excitatory input from other limbic structures and inhibitory input from the PFC [151; 160; 161]. The reward system promotes memory and repeat of critical pro-survival behaviors such as sex, eating, and social connections. Internet Pornography as Supranormal Stimulus High-speed, broadband Internet pornography is substantially more sexually arousing than other forms of pornography or fantasy and may become more immersive with three-dimen- sional technology. Novel sexual visuals trigger greater arousal, faster ejaculation, and more semen and erection activity than familiar visuals; arousal is further increased by ability to self- select material with ease. As an amplified mimic of stimuli with evolutionary salience that human brains have evolved to pursue, Internet pornography is a supernormal stimulus and unique activator of reward, impulsivity, and for some, addic- tion [151; 162; 163]. Pathologic Learning and Hyper-Reactivity Reward system vulnerability to pathologic learning can make Internet pornography use self-reinforcing. The neural sub- strates of sexual learning and addiction overlap. Development of addictive Internet pornography use promotes neuroplastic change. The mesolimbic dopamine system receives glutamate inputs from cortical and limbic regions. Glutamate synapses
associated with seeking and obtaining a specific reward become altered, enhancing mesolimbic dopamine system response to the specific reward. With the mesolimbic dopamine system sensitized to sexual reward, hyper-reactivity develops to Internet pornography cues [151; 163; 164]. Decreased Reward Sensitivity (Hypo-Reactivity) Reward system hyper-reactivity to Internet pornography cues develops concurrently with hypo-reactivity and down- regulation of response to natural rewards (i.e., partnered sex) [165]. Persons with addictive Internet pornography use show strong preferences for, but rapid habituation to, novel sexual images. This often fuels the search for even more novel sexual images and escalation to hardcore and extreme pornography, indicating decreased reward sensitivity, increased habitua- tion and tolerance, and greater stimulation needed for sexual arousal [151; 163; 164]. Addictive Internet pornography use is correlated with lower functional connectivity between the striatum and the PFC. Dysfunction in this circuitry is linked to behavioral choices that disregard potentially negative outcomes, including reduced executive control function during exposure to pornographic images [151; 166; 167; 168]. Sexual Conditioning and Dysfunction Sexual arousal conditioned to Internet pornography cues promotes sexual dysfunction [159]. Users crave the high levels of novelty, intensity, and arousal of Internet pornography that are difficult to sustain in partnered sex. When high stimula- tion expectations and requirements are not met, partnered sexual stimulation is ineffective. In some users, a preference for novelty arises from the need to overcome declining libido and erectile function, leading to conditioned preferences for Internet pornography use [169; 170]. Pornography use is inversely related to satisfaction with partners, as measured by affection, physical appearance, sexual curiosity, and sexual performance [171]. The caudate is involved in approach-attachment behaviors and motivational states associated with romantic love [172]. Putamen activation is associated with sexual arousal and penile tumescence [173]. Users of more extensive Internet pornography show smaller right caudate and lower putamen activation when viewing sexually explicit still photos. This reflects down-regulation of natural neural response to sexual stimuli from intense, prolonged exposure to pornographic stimuli [174]. Men with greater use of degrading or extreme pornography report more frequent concerns of sexual performance, penis size, and ability to maintain an erection (compared with moderate or non-users) [151; 175]. Early sexual conditioning impacts sexual arousal templates. A critical developmental period of sexual behavior forms around initial experiences with sexual arousal and desire, masturba- tion, intercourse, and orgasm. Younger age of onset for regular Internet pornography use and greater preference for pornog- raphy over partnered sex is associated with persistence of this
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