>lol you can't define narcissism
Simply put, narcissists are people who do not recognize the contributions of others, and do not see all the people who are infinitely more skilled or talented or valuable than they are. It's actually pretty easy to spot a narcissist.

Now, what underlying neuroscientific processes account for this? That, I am pretty sure, no one has found. Human beings are pattern-recognizing machines. It doesn't take a fundamental understanding of everything that makes up a human brain to recognize some of its patterns of behavior.