Brain structural characteristics of psychopathic traits and antisocial behaviors

Abstract

Introduction: Psychopathy is characterized by its shallow affect, callous lack of empathy or remorse and a parasitic and impulsive lifestyle. It is closely related to antisocial behaviors (Hare & Neumann, 2008). Previously, structural brain imaging studies examined the gray matter volumes (GMV) in various brain regions that were associated with psychopathy and antisocial behaviors. To be specific, it was shown that psychopathic traits were associated with brain structural abnormalities in both cortical and subcortical regions including striatum (Buckhotz et al., 2010) and insula (Ly et al., 2012). However, the volumetric findings regarding antisocial behaviors were mixed. On the other hand, cortical thickness analyses in psychopathy and antisocial behaviors received much less attention than the brain volumetric ones until recent years (Narayan, 2007). Previously, it was found that psychopaths had significantly cortical thinning in a number of brain regions including left insula (Ly et al., 2012). Nevertheless, prior studies suffered from four major limitations: psychopathy was studied as a categorical variable (Wahlund & Kristiansson, 2009); the specific part or side of hemisphere in the striatum or insula relating to psychopathy or antisocial behaviors was not examined; uni-modal neuroimaging method was applied; and sample size was small. The present study aimed to address the literature gap by examining the relationship of specific brain structural abnormalities in terms of cortical thickness and GMV with specific subtypes of psychopathy and antisocial behaviors. Methods: Eighty nine participants (38 murderers, 51 non-murderers) (77 males, 12 females) were recruited from Nanjing Brain Hospital in Nanjing, China. Murderers were detainees accused of homicide who were undergoing forensic psychiatric evaluation. Their structural magnetic resonance imaging (sMRI) data and psychopathic traits as well as IQ were measured. All sMRI data was acquired using a 1.5T GE Signa scanner with a single-shot gradient echo MPRAGE sequence (TR = 25 ms, TE = 6ms, field of view = 24 cm, matrix = 256 x 256, flip angle = 45°, thickness = 1.2 mm, 124 continuous sagittal slices without gap). Cortical thickness and volumetric segmentation was estimated using FreeSurfer software (FreeSurfer 4.0.5, http://surfer.nmr.mgh.harvard.edu) (Dale, Fischl, & Sereno, 1999; Fischl et al., 1999, 2002). Further manual tracing on volumetric segmentation was done using BrainSuite (Shattuck et al., 2002). Results: The cortical thickness analysis revealed significant differences (p< 0.05) in insula in murderers as well as in high psychopathy group. Specifically, cortical thinning in both left and right insula was found in murderers when compared to non-murderers, controlling for IQ and psychopathy factor. Also, it was found that high psychopathy group had significant greater cortical thickness in both left and right insula controlling for IQ and antisocial behaviors. Moreover, the correlations between cortical thickness in insula and psychopathy scores were significantly different between murderers and non-murderers (p< 0.05). Correlation sesults showed that murderers had significantly more psychopathic traits and reduced GMV in left caudate and total caudate (p< 0.05). In addition, positive correlations were only found between right putamen GMV and psychopathic traits, particularly for the total and factor one score of PCL-R (p< 0.05). Conclusions: Cortical thickness and gray matter volumetric (GMV) findings revealed that specific subtypes of psychopathic traits and antisocial behaviors were related to brain structural abnormalities in striatum GMV and insula cortical thickness. In particular, the brain volumetric findings suggested that the two components of striatum (caudate and putamen) were distinctly related to psychopathic traits and antisocial behaviors. These help us better understand the neural mechanisms in psychopathy and antisocial behaviors.