Psychopathy is a personality disorder defined by interpersonal, affective, lifestyle, and antisocial traits and behaviors, including grandiosity, egocentricity, deceptiveness, shallow emotions, lack of empathy, guilt, or remorse, irresponsibility, impulsivity, and a tendency to violate social norms (Hare, 2003). Psychopathic offenders are responsible for a disproportionate amount of antisocial behaviors, crimes and violence, and are overrepresented in correctional and forensic psychiatric institutions. Psychopathy is conceptually similar to the DSM-IV category of antisocial personality disorder (ASPD). However, the former places more emphasis on interpersonal and affective features, while the latter emphasizes overt antisocial behaviors. A proposal for DSM-V has been formulated (Miller and Holden, 2010), that includes features of psychopathy to be integrated within ASPD personality disorder. The standard tool for the assessment of psychopathy is the Psychopathy Checklist-Revised (PCL-R) (Hare, 2003). Although the PCL-R measures a unitary superordinate construct, confirmatory factor analyses of large data sets support a model in which psychopathy is underpinned by four correlated factors: the Interpersonal, Affective, Lifestyle, and Antisocial dimensions ( Hare, 2003 and Hare and Neumann, 2008).
An extensive literature on autonomic, neurophysiological and functional variables indicates that psychopathy is associated with difficulties in tasks requiring emotional and attentional processing, or the integration of cognitive and emotional information (Hare, 2003 and Newman et al., in press). These data indicate that limbic and paralimbic functions of individuals with psychopathy differ from those of normal subjects (Veit et al., 2002, Birbaumer et al., 2005 and Kiehl, 2006), and support the hypothesis of a possible morphologic involvement of the limbic–paralimbic circuitry (Kiehl, 2006 and Blair, 2007). Investigations of the cortical morphology of psychopathy or ASPD do find alterations in the orbitofrontal, ventromedial, cingulate and temporal paralimbic cortices, with some additional but less replicated regions of tissue reductions in the superior temporal gyrus, sulcus, and right dorsal cortices (Table S1). However, only one study (Yang et al., 2009a) used both the PCL-R for the selection of subjects, and the cortical pattern matching (CPM) pipeline (Thompson et al., 2004a), a technique allowing for maximum accuracy in the local mapping of cortical differences. Regarding the amygdala, a recent study found smaller global volumes in individuals with psychopathy (Yang et al., 2009b). Nonetheless, the amygdala tracings were made by two different raters, which may present a major source of inconsistency (Yang et al., 2009b). Moreover, although both studies by Yang et al. (Yang et al., 2009a and Yang et al., 2009b) assessed patients with the PCL-R, the exclusion of or correction for other psychiatric disorders, including those of the schizophrenia spectrum, reported in the original sample (Raine et al., 2000), is not mentioned in these two articles (Table S1).
In the present study we assessed brain morphology in a PCL-R psychopathy sample that was free of schizophrenia spectrum disorders. Larger white matter volumes were found in the parietal, occipital, and left cerebellar lobes of this sample with voxel-based morphometry (VBM) analysis, and lesser gray matter volumes were detected in parietal and paralimbic structures (Tiihonen et al., 2008). Here, we used two magnetic resonance imaging techniques, CPM (Thompson et al., 2004a) and the radial distance mapping (RDM) techniques (Thompson et al., 2004b), that allow more accurate mapping of the cerebral cortex and amygdala than allowed by VBM (Tiihonen et al., 2008). In fact, the first normalizes the brain, taking into account 40 manually traced sulci (Thompson et al., 2004a), and the second reconstructs the 3D shape of convex structures, from their coronal manual tracing (Thompson et al., 2004b). Spatial normalization and manual tracing by a single tracer were carried out for each technique. The a priori hypothesis was that structural differences would have been observed in the amygdala and in the most closely connected structures, belonging to the paralimbic network.
