Atypical nucleus accumbens morphology in psychopathy: another limbic piece in the puzzle

Abstract

Psychopathy has been associated with increased putamen and striatum volumes. The nucleus accumbens - a key structure in reversal learning, less effective in psychopathy - has not yet received specific attention. Moreover, basal ganglia morphology has never been explored. We examined the morphology of the caudate, putamen and accumbens, manually segmented from magnetic resonance images of 26 offenders (age: 32.5 ± 8.4) with medium-high psychopathy (mean PCL-R=30 ± 5) and 25 healthy controls (age: 34.6 ± 10.8). Local differences were statistically modeled using a surface-based radial distance mapping method (p<0.05; multiple comparisons correction through permutation tests). In psychopathy, the caudate and putamen had normal global volume, but different morphology, significant after correction for multiple comparisons, for the right dorsal putamen (permutation test: p=0.02). The volume of the nucleus accumbens was 13% smaller in psychopathy (p corrected for multiple comparisons <0.006). The atypical morphology consisted of predominant anterior hypotrophy bilaterally (10-30%). Caudate and putamen local morphology displayed negative correlation with the lifestyle factor of the PCL-R (permutation test: p=0.05 and 0.03). From these data, psychopathy appears to be associated with an atypical striatal morphology, with highly significant global and local differences of the accumbens. This is consistent with the clinical syndrome and with theories of limbic involvement.

Figure 1

Segmentation protocol for the striatum.

Figure 2

Significance maps of shorter (light blue to yellow color range) and larger (red color range) radial distances in the nucleus accumbens of 26 offenders with psychopathy compared to 25 controls. Maps were significant at correction for multiple comparisons (permutation test, left: p<0.003, right: p<0.006).

Figure 3

Significance maps of shorter (light blue to yellow color range) and larger (red color range) radial distances in the nucleus caudatus (top panel) and putamen (bottom panel) of 26 offenders with psychopathy compared to 25 controls. The ventral map of the right caudatus approached significance at the permutation test (p=0.06), while the dorsal map of the right putamen was significant at the permutation test (p=0.02).

Figure 4

Maps of local percent difference in the accumbens, caudate and putamen of the 26 psychopathy subjects compared to the 25 controls, compound in their reciprocal spatial positions. The global model allows to appreciate the entire morphology of the whole striatum in psychopathy.