Psychopathy has colored literature, film, and conversation for hundreds of years due to the stark difference that exists between it and a normal, healthy personality. The scientific community has been equally fascinated with this deceptive, antisocial, and violent subset of the population that strangely lacks empathy or true, deep emotion. Socially, psychopaths are prone to violent crime and have high rates of recidivism, so a deep understanding of the brain pathology of psychopaths is necessary for creating the best social policies. Past research has highlighted the involvement of the prefrontal cortex in some of the emotional and affective problems found in psychopaths, but recently scientists in Wisconsin found a strong neural correlate of the disorder: the synaptic connections between the ventromedial prefrontal cortex (vmPFC) and the amygdala and the medial parietal lobe.
Some of the most robust studies on the vmPFC's involvement in psychopathy come from lesion studies. Patients with lesions in this area exhibit a characteristic lack of empathy, irresponsibility, and poor decision-making that mirrors common symptoms of psychopathy. Since the vmPFC mediates executive functioning, its connections to other brain areas dealing with executive function and emotion are hugely important. Two such areas, the amygdala and part of the medial parietal lobe, the precuneus and posterior cingulate cortex (PCC), were the areas of interest in the Wisconsin imaging study published last month. Previous studies have examined the same pathways, but this study had larger sample sizes for each group and was even able to test two subtypes of psychopathy: primary, or low-anxiety, psychopathy and secondary, or high-anxiety, psychopathy. Researchers examined the structural integrity and functional connectivity of white matter between the vmPFC and the precuneus/PCC, as well as in the uncinate fasciculus (UF), the primary white matter pathway between the vmPFC and the amygdala, ultimately finding that psychopaths had both lower structural integrity and lower functional connectivity than non-psychopaths.
In order to test the hypothesis that the uncinate fasciculus had lower structural integrity in psychopaths, diffusion tensor imaging (DTI), was used. DTI is a type of magnetic resonance imaging that measures the diffusion force of water through neural tracts and yields fractional anisotropy (FA) scores, which are a measure of both fiber coherence and white matter integrity at the microstructural level. As expected, psychopaths had significantly lower FA scores (and thus lower structural integrity) than non-psychopaths in both whole-brain and UF-specific examinations.
Functional MRI at rest examinations were then utilized to test whether there is lower functional connectivity in one or both of these pathways from the vmPFC. Results showed lower correlations between the BOLD signals (a measure of glucose utilization) of the right anterior vmPFC and the right amygdala, showing lower functional connectivity in the vmPFC-amygdala pathway. Lower functional connectivity was also found between the right precuneus/PCC and the posterior vmPFC.
The DTI and fMRI procedures in this study produced convergent results to highlight the importance of the vmPFC-amygdala and vmPFC-precuneus/PCC pathways in producing some of the symptoms of psychopathy. The functional connectivity of the vmPFC-amygdala pathway was shown to differentiate between psychopaths and non-psychopaths as well as distinguish between high-anxiety and low-anxiety subtypes of psychopathy. There was significantly greater functional connectivity in low-anxiety psychopaths than high-anxiety ones.
Taken as a whole, the results of this recent study suggest a strong involvement of the vmPFC-amygdala and vmPFC-precuneus/PCC pathways in psychopathy. More research needs to be done on the subject utilizing larger samples, specific task studies for fMRI, and isolation of specific nuclei of the amygdala to determine the precise role these pathways play in this fascinating emotional disorder, but the recent study adds vital information to the study of psychopathy.