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Neurological mechanisms in psychopathy

Converging evidence suggests that the defi cits in emotional processing associated with psychopathy are linked to damage to the limbic system inhibiting the processing of emotional information. Laakso et al., for example, used brain imaging techniques to gain accurate data on the brain anatomy of 18 habitually violent psychopathic offenders. They found a strong negative association between the size of the hippocampus and scores on the PCL, suggesting that damage in this area, which is involved in the acquisition of conditioned fear, may explain the lack of fear associated with psychopathic behaviour. These data are added to by the fi ndings of Kiehl et al. (2001) who used brain imaging to study activity within the limbic system in response to an ‘affective memory task’. In it, three groups of participants (criminal psychopaths, criminal non-psychopaths and ‘normal’ controls) were asked to rehearse and remember lists of either neutral words or words describing negative emotions, and to identify these words in a subsequent recognition task. Psychopaths had signifi cantly less activity within their limbic systems and greater activation of the frontal lobes while processing negative emotional words than the other groups, suggesting that the psychopaths and nonpsychopaths used quite different brain systems to process emotional information. Birbaumer et al. extended this work to examine neurological processes while participants received painful pressure following presentation of various stimuli. The presentation of these stimuli before the pain meant that ‘normal’ participants learned to expect pain, reported some anxiety about these expectations, and developed a conditioned ‘pain’ response to these stimuli – evident through increased sweat gland activity when presented with the stimuli. During the acquisition phase of the study, they showed enhanced differential activation in the limbic–prefrontal circuit (amygdala, orbitofrontal cortex, insula and anterior cingulate). By contrast, psychopaths displayed no signifi cant activity in this circuit, no conditioned ‘pain’ response and reported no anxiety.

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