If a behavior is rewarded, it is more likely to be repeated. Orzack, a clinical psychologist at Mc Lean Hospital in Massachusetts claims that 40 percent of World of Warcraft (Wo W) players are addicted.
Brain function consequences Using an age- and gender-matched Chinese adolescent sample, Yan Zhou and associates (2009) demonstrate that IA adolescents have a lower gray matter density in the "left anterior cingulate cortex, left posterior cingulate cortex, left insula, and left lingual gyrus" than adolescents in the control group, indicating the presence of brain structural changes in Internet addicts.
Similar results have been confirmed by CB Weng and colleagues (2011) with a group of 17-year-olds who were diagnosed online game addiction (OGA) and another group without addiction.
An equivalent in World of Warcraft would be purple (epic) loot drops.
Players in World of Warcraft will often spend weeks hunting for a special item which is based on a chance system, sometimes with only a 0.01% chance of it being dropped by a slain monster.