Psychopathy is also correlated with higher levels of dopamine release in the brain, which makes sense as they get bored easily and do crazy shit to alleviate that boredom. In this experiment they had people fill out tests measuring psychopathic traits, and the higher someone scored the more dopamine was released when they were given amphetamine:
A lack of emotion isn't the only thing driving psychopaths. It now seems that their brains may overvalue the pleasure associated with getting what they want. In extreme psychopaths, this may result in callous and manipulative acts. Joshua Buckholtz , a neuroscientist at Vanderbilt University in...
www.newscientist.com
I'll tell you what else too, there are a lot more psychopaths out there than those who have a diagnosis. People tend to only be diagnosed with psychopathy if they're caught committing a serious crime, since the medical community doesn't tend to use that diagnosis in any widespread serious fashion, only the criminal justice system does (same as "insanity", it's a legal concept not a medical one). Therefore those who either don't get caught or don't break the law will likely never get a diagnosis. There's no way to know how many of those are out there, but the number is likely huge.
Same for sociopaths, generally the word sociopath refers to antisocial personality disorder which is in the DSM under cluster B same as borderline or narcissistic personality disorder, so that can technically be diagnosed by any psychiatrist but in practice a sociopath will not seek out that diagnosis because well why would they want that on their medical record? Same deal with most cluster B personality disorders.