MRIs of Psychopaths

From a Reddit comment:

[Researchers] have started taking scans of the brains of psychopaths while the patients view horrific images… When normal people view these images, fMRI scans light up to indicate heavy brain activity in sections of the emotion-generating limbic system, primarily the amygdala, which is believed to generate feelings of empathy. But in psychopathic patients, these sections of the amygdala remain dark, showing greatly reduced activity or none at all. This phenomenon, known as limbic underactivation, may indicate that some of these people lack the ability to generate the basic emotions that keep primitive killer instincts in check.

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