Some psychopaths may not be as fearless as previously thought, according to a new study in Frontiers in Psychology.

Psychopaths are individuals who exhibit antisocial personality traits, such as manipulation, deceitfulness, impulsive behavior and a lack of remorse. It is believed that psychopaths experience less fear than the average person.

“These symptoms have long been thought to reflect an overall lack of fear resulting from abnormal functioning of the amygdala,” said Douglas Schultz, principal investigator and corresponding author for the study. The amygdala is a set of neurons in the brain associated with fear.

Psychopathy is divided into two types. Primary psychopaths are thought to inherently have the traits associated with psychopathic behavior, while secondary psychopaths become that way as a result of repeated trauma or emotional reactions to negative events.

The current study assessed 50 white male prisoners aged 18 to 45. To determine psychopathy, researchers interviewed individual participants and placed them into groups, which included nine primary psychopaths, 10 secondary psychopaths and 31 controls.

Each participant was connected to machines to measure brain functioning and skin conductance. Using Pavlovian fear conditioning, participants viewed a continuous array of images, one of which was always associated with a 500 millisecond shock. Researchers examined participants’ brain and body responses to the images.

Results showed that the brain and body response was different based on whether the participant was a primary or secondary psychopath. Interestingly, primary psychopaths exhibited the same fear responses as the control group–increased activity in the amygdala and anterior cingulate cortex (ACC) as well as increased skin response. Secondary psychopaths exhibited the opposite reaction–inhibited amygdala and ACC activity–which is more typical of how psychopaths have been generally viewed.

“These results contradict the low-fear model of psychopathy and suggest that the low fear observed for psychopaths in previous studies may be specific to secondary psychopaths,” said Schultz.

The fascinating results indicate that not all psychopaths are created equal. Those who have inherent antisocial personality traits are still prone to the same fear responses as the average individual. Only psychopaths who have experienced repeated major stress and trauma appear to have inhibited fear.