Cognitive correlates of "pure apathy" in Parkinson's disease

Previous studies exploring the association between apathy and cognitive deficits in Parkinson's disease (PD) employed scales and questionnaires for apathy, which did not control for the possible confounding effect of motor symptoms. Here we investigated the cognitive correlates of "pure apathy" by the Dimensional Apathy Scale, which allows us to assess apathy minimizing the influence of motor symptoms.

Consecutive PD outpatients referred to our centre were screened. All participants underwent a neuropsychological battery to assess verbal memory, executive functions and visuospatial abilities, apathy and depressive symptoms.

We enrolled 56 non-depressed and non-demented PD patients, of whom 28 were apathetic and 28 were not. The two groups did not differ on demographic and clinical aspects; apathetic PD patients performed worse than non-apathetic PD patients on the part A, B and B-A of Trail Making Test and the interference task of Stroop test. No significant differences were found on memory and perceptual visuospatial tasks.

Our results demonstrated that "pure apathy" is associated with more severe executive dysfunctions such as alteration of set-shifting and inhibitory control, which are mediated by prefrontal cortex and subcortical regions (i.e. basal ganglia). Our findings also supported the hypothesis that co-occurrence of apathy and executive deficits may be the epiphenomenon of damage in prefrontal-striatal cortical circuitries connecting dorsolateral prefrontal cortex, anterior cingulate cortex and basal ganglia.