Damasio In Descartes Error

Investigation of the frontal lobe stems largely from the “Somatic Marker hypothesis” as outlined by Damasio in Descartes’ Error (Damasio 1994). It is often referred to as the prefrontal theory of psychopathy in neuroscience. The Somatic Marker hypothesis is based on the postulates that the prefrontal cortex is the region of the brain responsible for assigning values to options based on aggregated information made available to the prefrontal cortex by the integration of inputs from the rest of the central nervous system, and that if the prefrontal cortex is damaged then in the absence of this ability to contribute values in this manner is the cause of behaviours such as the indecision, irrationality and capriciousness that is often typical of

It is this nature that is often the root cause of reckless activity as there is no way for the psychopath to infer the ramifications of his actions prior to commitment to the action. The development of modern neuroimaging techniques have enabled investigation of this hypothesis.

Yang and colleagues studied the volume of prefrontal gray and white matter in psychopaths, using structural magnetic resonance imaging (MRI) in 16 unsuccessful psychopaths, 13 successful psychopaths and 23 control subjects (Yang et al., 2005). “Successful” and “unsuccessful” psychopaths were defined as psychopathic individuals that had evaded conviction for their crimes and those that had been convicted, respectively. All were assessed for psychopathic tendencies by use of the PCL-R. In the unsuccessful psychopaths, but not the successful psychopaths, yang et al found a 22.3% reduction in prefrontal gray matter volume compared with control subjects. It was also observed that PCL-R scores negatively correlated to prefrontal gray matter volume, but not to prefrontal white matter volume. This provides partial support

(2000) also assessed the prefrontal gray and white matter volumes using MRI in male volunteers with antisocial personality disorder and psychopathic-like behaviour, as well as the same metrics in healthy male subjects, male individuals with substance dependency, and psychiatric males diagnosed with schizophrenia spectrum disorders, affective disorders, anxiety disorders and other personality disorders that do not fall under the category of APD. In this manner they were able to study brain abnormalities in non-institutionalised violent offenders and also contrast the results of the MRI with those control groups with substance dependency and the psychiatric control group, allowing the authors to conclude that any differences discovered would not be attributable to psychological risk factors. The observed deficit was visually imperceptible at a clinical radiological level, but they recorded a significant reduction (11%) in prefrontal gray matter volume, but not white matter volume, comparing the APD group against the healthy male control group. The APD group showed a 14% reduction in prefrontal gray matter compared with the substance dependant group and also compared to the psychiatric control group. Raine and colleagues determined that these differences in gray matter volume correlated to the decision making processes in the APD group. However, once again the study did not identify a sub-region that was distinctly affected. Also, the groups were all male,