Narcissistic personality disorder (NPD) is one of 10 personality-based conditions defined by the American Psychiatric Association as mental health disorders.
People with NPD have a noted lack of ability to feel compassion or empathy, combined with a noted excess of self-regard. Current research indicates that these outward signs of a narcissistic personality are reflections of actual abnormalities within the brain.
For instance, according to a study published in 2013 the Journal of Psychiatric Research, NPD-affected individuals apparently have unusual thinness in the part of the brain responsible for producing empathy. They also have unusually high levels of activity in other key brain areas…
They also concluded that the degree of lost empathy in NPD patients matches up with the degree of thinness present in the abnormal cerebral cortex area.