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SHORT REPORTS |
Department of Psychology, University of Southern California
David Geffen School of Medicine at UCLA
Hillside Hospital, New York
Department of Psychology, University of Southern California
Department of Radiology, University of Southern California
David Geffen School of Medicine at UCLA, Los Angeles, California, USA
Correspondence: Dr Yaling Yang, Department of Psychology, University of Southern California, Los Angeles, CA 90089-1061, USA. Email: yalingy{at}usc.edu
Declaration of interest None. Funding detailed in Acknowledgements.
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ABSTRACT |
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INTRODUCTION |
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METHOD |
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Structural MRI was carried out on a 1.5-Telsa Philips S15/ACS (Selton, Connecticut, USA) scanner using three-dimensional T1-weighted gradient-echo scans (for detals see Yang et al, 2005). All image data-sets were processed with a series of preparatory steps before manual delineation of prefrontal subregions (Sowell et al, 1999, 2002). First, all images were anonymised to exclude personal information. Second, non-brain tissue and the cerebellum were removed from the brain volume, and signal intensity inhomogeneities were corrected (Sled & Pike, 1998). Third, fully automated tissue segmentation was applied and brain voxels were automatically classified as gray matter, white matter, or cerebrospinal fluid using a validated partial volume correction method (Shattuck et al, 2001). Finally, a spherical mesh surface was created using a three-dimensional active surface algorithm to facilitate identification of anatomical boundaries (MacDonald et al, 1994).
The parcellation of the prefrontal lobe into four subregions for each hemisphere followed the methods of Ballmaier et al (2004). A three-dimensional shape representation and coronal two-dimensional MRI scan of the segmentation of the prefrontal cortex of one of the participants are shown in the data supplement to the online version of this paper. All anatomical delineations were conducted by two research assistants trained by Y.Y. Unlike gray matter subregions, which are clearly defined by sulcal landmarks, white matter delineations are arbitrary and the segmentation results should be viewed as estimated volumes. To assess interrater reliability, all anatomical regions were delineated on ten randomly chosen image data-sets; intraclass correlation coefficients ranged between 0.90 and 0.97 for gray matter and white matter in all four frontal subregions. Each of the eight subregional volumes was divided by total intracranial volume to account for potential differences in individual brain size. Since there was a lack of hemisphere effect, white matter volumes from two hemispheres were averaged to create a mean regional volume.
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RESULTS |
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2=0.29). Groups
differed in the volume of white matter in the inferior (F(2,
41)=11.09, P=0.001), middle (F(2, 41)=7.05,
P=0.003) and orbitofrontal cortex (F(2, 41)=6.87,
P=0.001), with increased white matter in liars. However, a trend
towards lower white matter volume was found in the superior frontal cortices
for liars (F(2, 41)=0.42, P=0.66). Liars showed
significantly increased white matter in inferior, middle and orbitofrontal
cortex compared with both antisocial controls (P=0.001,
P=0.004, and P=0.006, respectively) and normal controls
(P=0.001, P=0.005, and P=0.001 respectively;
Fig. 1). No difference was
found for gray matter volume in the four subregions (F(8, 78) =0.54,
P=0.82).
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DISCUSSION |
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One interpretation of the white matter increases in the ventral and lateral nonsuperior frontal regions could be that a pre-existing variation in prefrontal structure may predispose individuals to engage in pathological lying. Alternatively, several studies have argued that long-term training may induce regional increases in white matter volume (Schmithorst & Wilke, 2002; Bengtsson et al, 2005). In the case of lying, it is conceivable that excessive lying repeatedly activates the prefrontal circuit underlying lying, resulting in permanent changes in brain morphology. This Pinocchios nose hypothesis of pathological lying could be compared with the competing predispositional hypothesis using a prospective longitudinal study assessing both white matter volume and degree of lying from childhood to adulthood.
The engagement of ventral and lateral prefrontal regions in lying may be anticipated from fMRI studies, several of which have associated these regions with executive functions crucial to successful deception, including decision-making, moral reasoning, rule maintenance/retrieval and response inhibition (Bunge, 2004). Although some studies showed partial activation in the superior frontal cortex when lying involved a non-vocal motor response (Langleben et al, 2002, 2005), this region is more associated with functions less directly linked to deception, such as spatial information processing, attention reorientation and novelty detection (Gomot et al, 2006). Conversely, gains in white matter volume in these prefrontal regions (in the absence of gray matter reduction) may lead to faster sharing of information within frontalcortical circuits in pathological liars. Thus, increased white matter in these subregions of the prefrontal cortex in liars may predispose to maintaining a lifestyle of pathological lying and malingering. The use of advanced imaging techniques such as diffusion tensor imaging to assess neural connectivity (Nakamura et al, 2005) may allow more thorough investigation of the subtle abnormalities responsible for pathological lying.
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ACKNOWLEDGMENTS |
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REFERENCES |
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Received for publication April 5, 2006. Revision received July 23, 2006. Accepted for publication October 3, 2006.
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