However, psychopaths fare strangely well on tests of empathy. Given that these tests are usually based on self-reports and that psychopaths are prolific liars, this is not necessarily surprising. But psychopaths also produce intriguing results on experiments that test physiological and brain responses. Skin conductance, for example, measures how good a conductor of electricity your skin is; it’s a good indicator of your emotional state, since when you sweat in response to stress, fear or anger, your skin becomes momentarily better at carrying electric current. As you might expect, when psychopaths are exposed to pictures of people in distress, they show less skin conductance reactivity than do non-psychopaths. Other tests measure startle responses: if you show a person pictures that they find threatening, they startle much more easily in response to loud sounds. Psychopaths respond normally to direct threats, such as an image of the gaping jaw of a shark or a striking snake, but not to social threats, such as people in pain or distress. Ordinary people react to both.
Neuroscientists have also studied the empathic responses of psychopaths. In typical studies involving functional magnetic resonance imaging (fMRI), the areas of the brain associated with empathy don’t activate in psychopaths to the same degree as in control subjects. But when the neurobiologist Harma Meffert and colleagues from the University of Groningen in the Netherlands explicitly instructed them to ‘feel with’ a hand that is being caressed or shoved aside, the researchers discovered that psychopaths were able to muster a normal response. In other words, when explicitly told to empathise with another, psychopaths could do it.