Editor's Note: Dr. David Eagleman directs the Eagleman Laboratory for Perception and Action at Baylor College of Medicine in Houston. He is the subject of Sunday's episode of "The Next List," on CNN at 2 p.m. ET.

By David Eagleman, Special to CNN

(CNN) - In the wake of the Aurora, Colorado, movie theater shooting, many people are asking the same questions: What kind of derangement is revealed by the alleged acts of James Holmes, who has been charged with murder and attempted murder in a massacre during a showing of "The Dark Knight Rises"? What is wrong with the brain that concocted this plot? How will information about Holmes' mental state play out in the courts?

My goal here is to bring a perspective on this tragedy from the point of view of a neuroscientist.

Few facts are publicly available about Holmes’ mental health background. Despite the dearth of data, however, several issues can be clarified and discussed.

To begin, it’s critical to understand the difference between two words: psychotic and psychopathic. These are two similar-sounding terms that commentators sometimes use interchangeably.

But, in reality, they are entirely different.

A person with a psychosis is disconnected from reality. For example, a homeless person arguing with himself is typically suffering from a psychosis such as schizophrenia. Someone with this sort of mental illness is termed “psychotic.” A person with a disorder of mood such as bipolar disorder (in which one alternates between depression and mania) can also have associated psychotic features such as hallucinations and delusions.

In contrast, a person with psychopathy has low empathy and low remorse. The psychopath can be smart, glib, charming and blend in perfectly with the society around him, but he lacks compassion and guilt. Behind his “mask of sanity” lurks a manipulative creature who can hurt others without compunction. A psychopath (or, synonymously, a sociopath) is someone like Jeffrey Dahmer or Ted Bundy. They are termed “psychopathic”.

Which, if either of these, was Holmes? If convicted of the crimes, did he suffer from a psychosis, or was he instead a cognitively intact but emotionless sociopath? When Colorado Rep. Ed Perlmutter told the media that Holmes was “a psychotic son of a bitch," it’s safe to guess that his statement stemmed from a confounding of the terms rather than a specific diagnosis.

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