Recent research suggests that engaging in sadistic sexual behaviors is driven by a desire for feelings of power and dominance, in addition to simply sexual pleasure. This is true for those in the general population with a sexually sadistic fetish and for those with a severe enough condition to be diagnosed with sexual sadism disorder.
According to an fMRI brain scan of 15 violent sexual offenders, sadists showed greater amygdala (a part of the brain associated with sexual arousal) activation when viewing images depicting pain. Sadists also rated these images as showing higher levels of pain than did non-sadists in the group. Further, sadists showed more activity in anterior insula (a pain processing part of the brain) than did non-sadists.