Once the reward centre is altered, a person will compulsively seek out the activity or place that triggered the dopamine discharge. (Like addicts who get excited passing the alley where they first tried cocaine, the patients got excited thinking about their computers.) They crave despite negative consequences. (This is why those patients could crave porn without liking it.) Worse, over time, a damaged dopamine system makes one more "tolerant" to the activity and needing more stimulation, to get the rush and quiet the craving. "Tolerance" drives a search for ramped-up stimulation, and this can drive the change in sexual tastes towards the extreme.
The most obvious change in porn is how sex is so laced with aggression and sadomasochism. As tolerance to sexual excitement develops, it no longer satisfies; only by releasing a second drive, the aggressive drive, can the addict be excited. And so for people psychologically predisposed there are scenes of angry sex, men ejaculating insultingly on women's faces, angry anal penetration, etc. Porn sites are also filled with the complexes Freud described: "Milf" ("mothers I'd like to fuck") sites show us the Oedipus complex is alive; spanking sites sexualise a childhood trauma; and many other oral and anal fixations. All these features indicate that porn's dirty little secret is that what distinguishes "adult sites" is how "infantile," they are, in terms of how much power they derive from our infantile complexes and forms of sexuality and aggression. Porn doesn't "cause" these complexes, but it can strengthen them, by wiring them into the reward system. The porn triggers a "neo-sexuality" an interplay between the pornographer's fantasies, and the viewer's.
