Sociopathy: Fear: Deficient fear conditioning in psychopathy: a functional magnetic resonance imaging study.

Entrez PubMed: "Psychopaths belong to a larger group of persons with antisocial personality disorder and are characterized by an inability to have emotional involvement and by the repeated violation of the rights of others. It was hypothesized that this behavior might be the consequence of deficient fear conditioning.
The healthy controls showed enhanced differential activation in the limbic-prefrontal circuit (amygdala, orbitofrontal cortex, insula, and anterior cingulate) during the acquisition of fear and successful verbal and autonomic conditioning. The psychopaths displayed no significant activity in this circuit and failed to show conditioned skin conductance and emotional valence ratings, although contingency and arousal ratings were normal. CONCLUSION: This dissociation of emotional and cognitive processing may be the neural basis of the lack of anticipation of aversive events in criminal psychopaths."

Birbaumer N, Veit R, Lotze M, Erb M, Hermann C, Grodd W, Flor H.
Deficient fear conditioning in psychopathy: a functional magnetic resonance imaging study.
Arch Gen Psychiatry. 2005 Jul;62(7):799-805.