Anhedonia and executive functions in PD
Anhedonia is an inability to experience pleasure from normally pleasurable life events such as eating, exercise, or social or sexual interaction. Findings about the relationship between anhedonia and frontal lobe dysfunctions are discordant. Isella et al.  carried out a study to formally assess the prevalence and correlates of physical anhedonia in PD patients compared with normal controls. They found higher levels of anhedonia in PD patients with respect to controls and no significant association of physical anhedonia with clinical or neuroradiological features or frontal lobe dysfunction. However, others found that in both PD and progressive supranuclear palsy, anhedonia assessed using the Snaith-Hamilton Pleasure Scale was associated with frontal lobe dysfunction as evaluated by means of the Frontal Assessment Battery [47, 48], a short neuropsychological tool that assesses executive functions at the bedside. In 2013 a study reported that in patients with MD anhedonia was associated with impaired divided attention and also with a degree of apraxia and impairment of verbal memory . Since current findings about the relationship between anhedonia and frontal lobe dysfunction are conflicting, this question needs further investigation.
In PD, executive dysfunction is associated with depression, apathy, and anhedonia, though there is no clear-cut agreement on the causative relationship between cognitive and affective disorders. It is conceivable that they share a common neurochemical and neuroanatomical background consisting of degeneration of the mesocortical and mesolimbic dopaminergic projections. In the PD population a subgroup of patients may be identified as having specific characteristics: more severe executive dysfunction associated with apathy/anhedonia and depression, and increased risk for dementia. Thus, evaluations of both neuropsychological profile and the presence of depressed mood, apathy, and anhedonia should be regarded as a routine procedure for predicting prognosis and decision-making with regard to treatment.