Apathy and executive functions in PD
Apathy is a primary loss of motivation, interest, and effortful behaviour. Studies in PD patients have shown that the presence of apathy is specifically associated with frontal lobe dysfunction. Starkstein et al.  found that PD patients with apathy performed worse than PD without apathy on part B of the Trail Making Test and lexical fluency task. Consistently, Pluck and Brown  found that PD patients with apathy showed decreased performance compared with PD patients without apathy on tasks evaluating specific frontal lobe functions including verbal fluency, changing mental categories, and inhibition. Isella et al.  confirmed the relationship between apathy and frontal lobe dysfunction in PD patients; they found that PD patients with apathy showed a poorer performance than PD patients without apathy on tasks assessing verbal fluency set- shifting, sensitivity to interference, and ability to inhibit automatic behaviour. More recently, Zgaljardic et al.  demonstrated that patients with significant levels of apathy performed worse than patients with low apathy scores on measures of verbal fluency and verbal and nonverbal conceptualization. Low performance on cognitive tasks assessing verbal fluency, working memory, verbal abstraction, and executive dysfunction significantly predicts both the presence and the worsening of apathy. More recently, Varanese et al.  found that apathy was associated with deficits in implementing efficient cognitive strategies: patients with apathy had poorer performance than patients without apathy in immediate recall and executive tasks. Grossi et al.  found that apathy is characterized by a similar neuropsychological profile in patients with dementia regardless of the pathology (PD or Alzheimer’s) responsible for the dementia. In both diseases apathy was found to be associated with defects on frontal tasks, thus strongly supporting the existence of an ‘apathetic syndrome.
Although apathy is generally considered to occur in advanced disease stages, studies have found a prevalence rate of 22.9% in de novo PD patients . In a longitudinal study, apathy was found to be a predictor of the development of dementia. Conversely, dementia at baseline, a more rapid decline in speech and axial impairment , and poor performance on the interference task of the Stroop Test  may predict development of incident apathy in PD patients.