Atypical nucleus accumbens morphology in psychopathy: Another limbic piece in the puzzle
Introduction
Psychopathy is a personality disorder characterized by shallow affect, a callous lack of empathy or remorse, and an inclination to a parasitic and impulsive lifestyle, often leading to criminal behavior (Hare & Neumann, 2008).
Recent research on brain morphology has detected morphological differences in the brain structures of individuals with psychopathy, although differences in the methods used have led to inconsistent results (Koenigs, Baskin-Sommers, Zeier, & Newman, 2010). Differences have been reported in cortical and subcortical regions (Boccardi et al., 2011, de Oliveira-Souza et al., 2008, Muller et al., 2008, Tiihonen et al., 2008, Yang, Raine, Colletti, Toga and Narr, 2009). Among these, the basal ganglia are crucial for emotional processing and behavioral planning, particularly via their connections with the amygdala and the frontal lobe, within the limbic circuit (Devinsky et al., 1995, Vogt et al., 1992). Indeed, the hypothesis that psychopathic behavior may correlate with differences in the limbic structures and connections has been repeatedly corroborated (Craig et al., 2009, Kiehl, 2006, Raine et al., 2010).
Some morphometric studies have found striatal volume alterations in conditions associated with violent behavior. One study found greater global volumes of the putamen in a group of subjects with antisocial personality disorder (ASPD) subjects (Barkataki, Kumari, Das, Taylor, & Sharma, 2006), which was interpreted as possibly related to impulsivity and poor behavioral control. A second study (Glenn, Raine, Yaralian, & Yang, 2010) examined the volume of the entire striatum, of the nucleus lenticularis (putamen and pallidus), and of the caudate head and body, in psychopathy. It found a 9.6% increase for the whole striatum, and similar enlargement of the nucleus lenticularis, bilaterally; findings were interpreted as connected to the increased stimulation seeking and impairments in reinforcement learning in psychopathy. A recent voxel-based morphometry (VBM) study detected greater local gray matter volume in the right caudate and in the left accumbens nuclei in offenders with sub-threshold psychopathy scores (Schiffer et al., 2011).
Nonetheless, only global volumes, or local gray matter density in voxel-based analyses, were examined, and information on the actual 3D shape of the basal ganglia is lacking to date. Moreover, the previous studies did not carry out specific region-of-interest analyses for the nucleus accumbens, the critical basal ganglia nucleus connecting to the amygdala and the orbitofrontal cortex within the anterior limbic circuit (Devinsky et al., 1995, Vogt et al., 1992), which is known to be involved in psychopathy (Boccardi et al., 2011, de Oliveira-Souza et al., 2008, Kiehl, 2006, Raine et al., 2010, Yang, Raine, Narr, Colletti and Toga, 2009). The accumbens is a key structure in reversal learning, i.e., the ability to overwrite on previously learned knowledge as context conditions change. Particularly, individuals need to take experience into account, and update the values that they attributed to stimuli or goals, as well as knowledge about the effects of their own behavior. A goal, or a behavior, that turned out to be good value in the past may not be worth or useful in a different time or context, so the individual must overwrite on prior knowledge in order to engage in more adaptive actions. Considering the limited ability of people with psychopathy to learn from experience, and that many are refractory to different kinds of treatment or correctional contexts, the accumbens is a particularly interesting target for neuroscientific investigation, to assess the neurobiological correlates of the cognitive and volitional capacities generating behavior in psychopathy.
Here we aimed to quantify the global volume of the caudate, putamen and accumbens nuclei, and to map local morphological differences using the radial distance mapping algorithm. We examined a sample of criminal offenders with psychopathy as defined by the Psychopathy Checklist Revised (PCL-R), lacking disorders in the schizophrenia spectrum, which are associated with independent brain alterations in individuals with violent behavior (Narayan et al., 2007).
Section snippets
Subjects
Study subjects with psychopathy, already described in detail (Boccardi et al., 2010, Boccardi et al., 2011, Tiihonen et al., 2008), included 26 habitually violent male offenders, consecutively admitted to a university forensic psychiatric hospital for pre-trial assessment, and currently charged with a violent offence. They fulfilled criteria for DSM-IV ASPD and ICD-10 dissocial personality, had no history or current diagnosis of psychosis or schizotypal personality disorder, had additional
Results
Offenders scored highly on the PCL-R evaluation; the mean group score was 29.9 ± 5.2. When subjects were divided into those above and below a score of 30 on the PCL-R, the 14 subjects scoring lower than 30 still had a PCL-R mean score of 25.9 (± 2), compatible with medium severity of psychopathy. The 12 subjects with high psychopathy differed significantly from the 14 with medium psychopathy on Factor 1 (Interpersonal), Factor 2 (Affective), and Factor 4 (Antisocial, please see Table 1).
Experimental findings
We compared the 3D morphology of the accumbens, caudate and putamen nuclei in a sample of criminal offenders with psychopathy. These subjects were not affected by disorders of the schizophrenia spectrum, and were compared to controls of same gender and similar age. These nuclei exhibited an atypical morphology, consisting in complex patterns of local enlargement and reduction. The different morphology of the nucleus accumbens was highly significant even after correcting for multiple comparisons.
Conclusions
This study detects a peculiar striatal morphology, characterized by severe hypotrophy of the nucleus accumbens, in offenders with psychopathy. Replication is required due to many limitations of the study. Anyway this finding is consistent with the clinical and neuropsychological features of psychopathy, as well as the known unresponsiveness to treatment or correction of these subjects.
Psychobiological correlates of psychopathy point to the involvement of the paralimbic network, a set of
Conflict of interest
None of the authors had any interest competing with the present work.
Acknowledgments
P.T. is supported in part by NIH grants EB008281, RR013642, and AG020098.
The opinions expressed in this article are those of the authors alone and should not be interpreted as having been endorsed by the National Institutes of Health.
This work was also supported by AFaR (Associazione Fatebenefratelli per la Ricerca).
We thank Enrica Cavedo, who served as reference for the computation of the inter-rater ICC values for the examined nuclei.
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