A community sample of males (n=72) between ages 21 and 45 years were recruited from five temporary employment agencies. The only exclusion criteria were nonfluency in English, history of epilepsy, claustrophobia, pacemaker, and metal implants; participants were not screened for psychopathy or criminal behavior prior to entry in the study. The University of Southern California Institutional Review Board approved the study. Participants were informed that the purpose of the study was to examine various correlates of antisocial behavior. After complete description of the study to the subjects, written informed consent was obtained.
Psychopathy was assessed using the Psychopathy Checklist – Revised (PCL-R; Hare, 1991
), supplemented by five sources of collateral data – the Interpersonal Measure of Psychopathy (Kosson et al., 1997
), self-reported crime as assessed by an adult extension of the National Youth Survey self-report delinquency measure (Elliot et al., 1983
), official criminal records and data derived from the Structured Clinical Interview for the DSM-IV mental disorders (SCID-I and SCID-II; First et al., 1996
; First et al., 1997
). To maximize confidentiality and minimize denial of self-report crime, a certificate of confidentiality was obtained from the Secretary of Health and Human Service under section 303 (a) of the Public Health Act 42. Scores on the two overarching factors of the PCL-R were also calculated to determine whether there may be volumetric differences specific to one factor or the other. Factor 1 represents the interpersonal and affective characteristics of psychopathy (e.g., glibness, superficial charm, pathological lying, shallow affect, lack of guilt, or remorse). Factor 2 represents the antisocial traits and behaviors (e.g., impulsivity, stimulation seeking, juvenile delinquency).
In order to compare individuals scoring higher and lower in psychopathy, we formed high and low groups. A cutoff score of 23 and above on the PCL-R was used for membership into the high-scoring (psychopathic) group (n
= 24), maintaining consistency with prior studies (Ishikawa et al., 2001
; Raine et al., 2003
; Yang et al., 2005
). The low-scoring group (controls) was designated as individuals scoring in the bottom third (0–14) on the measure (n
= 24). Descriptive statistics for the two groups are provided in .
Comparisons Between the Control and Psychopathic Groups on Demographic and Psychopathy Measures
For MRI acquisition and processing, 128 three-dimensional T1-weighted gradient-echo 1.7 mm coronal slices were obtained using a 1.5-T scanner (model S15/ACS; Phillips, Shelton, Conn.), with matrix 256 × 256, field of view= 24 cm, TR= 34 ms, TE = 12.4 ms, flip angle= 35°, taken directly orthogonal to the anterior – posterior commissure line.
The anterior cingulate and its subregions were measured manually by one of the authors (ALG) blind to group status, by summing the total area measurements across all slices and multiplying by slice thickness. All volumetric measures were obtained in the coronal plane. Boundaries were based on the protocol by the Laboratory of Neuro Imaging (LONI) at the University of California, Los Angeles (http://www.loni.ucla.edu/~esowell/edevel/MedialLinesProtocol.htm
) and by Rademacher et al. (1992)
. The division between dorsal and ventral ACC was based on Bush et al. (2000)
. Boundaries for defining the dorsal anterior cingulate segmentation were as follows and are depicted in : posterior – the point at which the paracentral sulcus interrupts the cingulate sulcus; anterior – the coronal slice in which the most anterior part of the corpus callosum becomes visible; inferior – callosal sulcus; superior – cingulate sulcus. Boundaries for defining the ventral anterior cingulate were as follows: posterior boundary – the first coronal slice in which the anterior part of the corpus callosum can no longer be seen; anterior boundary – the cingulate sulcus; inferior boundary – the cingulate gyrus, in the event that it extends to the region inferior to the genu of the corpus callosum (if not, the first full gyrus ventral to the corpus callosum is the inferior boundary and is connected to the superior boundary); superior boundary – the cingulate sulcus. The anterior cingulate gyrus (dorsal and ventral) is bounded laterally by white matter. The test-retest reliability for the rater was found to be 0.94 using ten different scans.
The anterior cingulate and its subregions. Left: Sagittal slice depicting the division between the dorsal and ventral subregions. Right: Coronal slices were used for tracing the subregions.
We used analysis of variance (ANOVA) to test for volumetric differences between the two groups in total anterior cingulate volume, and the volume of the dorsal and ventral subregions. Univariate ANOVAs with whole brain gray matter as a covariate were used to determine whether this factor affected results. Group analyses were followed up by correlational analyses including all 72 participants. Multiple regression was used to enter age as a covariate to determine whether this affected results.