Click on the following: Psychopathy: an Audio Discussion taking place at the University of Pennsylvania.
Summary of the audio presentation by Robert Winer, M.D.
Brain imaging "shows" that murders have less well functioning or working pre-frontal cortex, (PFC) which controls the more aggressive limbic system. All brain imaging work is correlational. Neurologists who performed selective lesions of ventro-medial PFC were able to demonstrate blunted emotional response, disinhibited, etc. in the subjects. Current studies use the term "fear conditioning" to describe the so-called normal ability to predict in childhood that certain stimuli predictable result in punishments and that the thought of these punishments or the actual punishments are associated with feelings of anxiety and nervousness. This researcher defines conscience as "a set of classically-conditioned emotional responses, coming from the ability in childhood to associate stimuli that reliably predict punishments". What he means is that when, in childhood, you broke a rule it was predictably followed by punishments.