The impact of executive dysfunctions on Theory of Mind abilities in Parkinson's disease.

Theory of Mind (ToM) is the ability to infer and reason about others' mental states, a process impaired by Parkinson's disease (PD). ToM performance in PD seems to be strongly related to executive functioning but the exact nature of this relationship is still unclear. We aim to investigate the direct impact of several executive dysfunctions on ToM deficits (Affective and Cognitive ToM) in PD patients. Sixty-eight PD patients underwent neuropsychological tests evaluating executive control such as inhibition, cognitive flexibility, processing speed or working memory and Cognitive and Affective ToM. We divided participants into two groups based on their performance on executive tests: PD patients with poor executive functioning (PD-EF-) and those with preserved executive functioning (PD-EF+). To explore the direct impact of executive subdomains on ToM abilities, two mediation models were executed in the whole sample. We found that PD patients with poor executive functioning reported poorer scores on Affective and Cognitive ToM tasks than PD patients with preserved executive functions, controlling for age and education. Moreover, parallel mediation models, conducted in the whole sample, indicated that performance on phonological fluency mediated the relationships between educational level and both Affective and Cognitive ToM, controlling the effect of other executive tests. These findings further support the idea that executive functions are crucial in ToM processes. Particularly, phonological fluency, whose execution requires both verbal abilities and cognitive flexibility, mediated ToM performance controlling the effect of other executive functions. The identification of neuropsychological processes underpinning ToM abilities might represent a plausible target for cognitive training to strengthen ToM abilities in PD.

The role of the motor subtypes on the relationship between anxiety and cognitive dysfunctions in Parkinson's disease.

Anxiety is a common neuropsychiatric symptom in Parkinson's disease (PD). Until now, anxiety has been consistently related to cognitive deficits and severity of motor symptoms, whereas the association between anxiety and motor subtypes (TD-PD, tremor dominant and PIGD-PD, postural instability/gait disturbances dominant) revealed contrasting results. The present study aims to investigate the relationship between PD motor subtypes and anxiety and to explore whether the relationship between anxiety and cognitive deficits occurs in a specific PD motor subtype. Consecutive PD outpatients were recruited and divided into TD-PD and PIGD-PD groups according to Jankovic et al.'s criteria. All participants underwent a neuropsychological battery to evaluate anxiety, apathy, the global cognitive functioning, memory abilities, executive and visuo-constructional functions. Thirty-six patients with TD-PD and 35 patients with PIGD-PD were enrolled. The two groups did not differ on demographical and clinical variables. As for the severity of anxiety, no significant difference between the two groups was found. Regression analysis revealed that higher anxiety score was associated with poorer performance on constructional visuospatial test in both TD-PD and PIGD-PD. Clinical variables were not associated with anxiety in the two groups. Our findings indicated that the severity of anxiety was not associated with any PD motor subtypes. Moreover, regression analysis revealed that impaired visuo-constructional abilities are related to anxiety independently of PD motor subtypes. Since altered fronto-parietal network might be one of the pathogenetic mechanisms underpinning anxiety and constructional visuospatial deficits, the treatment of cognitive dysfunctions might reduce anxious symptoms.

Prospective memory in Parkinson's disease: the role of the motor subtypes.

BACKGROUND: Prospective memory (PM) is defined as memory for future intentions and it is typically divided into time-based and event-based PM. Deficit of PM has been reported in patients with Parkinson's disease (PD) but no study has yet explored the association between motor subtypes (tremor dominant and rigidity/bradykinesia dominant) and performance on PM tasks. The aim of the study was to explore the role of motor subtypes in the defect of PM. METHODS: Consecutive outpatients with tremor dominant (TD-PD) or rigidity/bradykinesia dominant (PIGD-PD) PD and healthy subjects (HCs) were enrolled and underwent a neuropsychological battery assessing PM, verbal memory and executive functions and questionnaires assessing apathy, functional autonomy, and perceived memory disturbances. RESULTS: We enrolled 28 patients with TD-PD, 28 patients with PIGD-PD and 50 HCs. The three groups did not differ on demographic and cognitive variables. Patients with TD-PD performed worse on time-based PM tasks than patients with PIGD-PD and HCs; no significant difference was found among the three groups on event-based PM tasks. Executive dysfunctions contributed to reduced time-based PM scores in TD-PD. Moreover, severe deficit of time-based and more frequency of perceived failures of PM contributed to reduced functional autonomy in TD-PD. CONCLUSION: The finding of a poorer performance of patients with TD-PD than ones with PIGD-PD and HCs suggests a selective deficit of time-based PM abilities in TD-PD group; therefore, deficit of time-based PM might be considered as a distinctive non-motor symptom of TD-PD and it might affect the functional autonomy in this subtype of PD.