Do parkinsonian patients have trouble telling lies? The neurobiological basis of deceptive behaviour

Abstract

Parkinson's disease is a common neurodegenerative disorder with both motor symptoms and cognitive deficits such as executive dysfunction. Over the past 100 years, a growing body of literature has suggested that patients with Parkinson's disease have characteristic personality traits such as industriousness, seriousness and inflexibility. They have also been described as 'honest', indicating that they have a tendency not to deceive others. However, these personality traits may actually be associated with dysfunction of specific brain regions affected by the disease. In the present study, we show that patients with Parkinson's disease are indeed 'honest', and that this personality trait might be derived from dysfunction of the prefrontal cortex. Using a novel cognitive task, we confirmed that patients with Parkinson's disease (n = 32) had difficulty making deceptive responses relative to healthy controls (n = 20). Also, using resting-state (18)F-fluorodeoxyglucose PET, we showed that this difficulty was significantly correlated with prefrontal hypometabolism. Our results are the first to demonstrate that the ostensible honesty found in patients with Parkinson's disease has a neurobiological basis, and they provide direct neuropsychological evidence of the brain mechanisms crucial for human deceptive behaviour.

Figure 1

Proportion of correct honest (Truth condition) and deceptive (Lie condition) responses during the deception task in the Parkinson's disease patients and normal controls. Error bars represent standard error. PD = Parkinson's disease.

Figure 2

(A) Brain regions showing hypometabolism in the Parkinson's disease patients compared with the normal controls. Note that the statistical threshold was relatively liberal in this group comparison (P < 0.05, uncorrected), since this analysis was done only for generating a mask image included in the cognitive-metabolic correlation analysis within the group of Parkinson's disease patients. The regions are displayed on a surface-rendered standard brain. (B) Brain regions showing a significant correlation between performance in the deception task and regional cerebral glucose metabolism in the Parkinson's disease patients (P < 0.001, uncorrected). Note that the results were masked with the above contrast of the normal controls versus the Parkinson's disease patients to confine our analysis to the regions showing hypometabolism in the Parkinson's disease patients. The possible confounding effects of age and sex were also controlled. (C) Scatter plots of the correlations between the deception task indices and the FDG-uptake values in the right anterior prefrontal cortex (r = –0.719, P < 0.001) and the left dorsolateral prefrontal cortex (r = –0.709, P < 0.001). FDG = fluorodeoxyglucose; PD = Parkinson's disease.