Social Cognition Across the Parkinson’s Disease Cognitive Spectrum

Background: Parkinson’s disease (PD) is a multi-system neurodegenerative disorder associated with a range of symptoms, including cognitive deficits. Impairments have been reported across all cognitive domains, and more recently, socio-cognitive functions have gained attention. Theory of mind (ToM) and facial emotion recognition (FER) are the two most investigated components of social cognition (SC). There is evidence of deficits in both functions in PD. The aim of this dissertation is to analyze the presence and prevalence of SC deficits in cognitively unimpaired PD patients (PD-NC), with mild cognitive impairment (PD-MCI), and dementia (PDD), compared to cognitively healthy controls (HC). Methods: Sixty-one PD patients underwent a comprehensive (II-level) neuropsychological assessment (i.e., including at least two tests for each cognitive domain) according to the Movement Disorders Society PD-MCI (Litvan et al., 2012) and dementia (Emre et al., 2007) guidelines. While 50 HC, included as control group were evaluated through a I-level cognitive assessment, which comprised a screening of global cognitive functioning along with one test per cognitive domain (Dunne et al., 2021). SC abilities were measured by the FACE (FAcial Complex Expression) test (Terruzzi et al., 2023), that evaluates facial complex mental states recognition abilities, and the Story-based Empathy Task (SET) (Dodich et al., 2015), that assesses both cognitive and affective ToM. Results: Between-group comparisons indicated significant differences for each domain of cognition among groups, with the exception of PD-NC and HC in the majority of the evaluated cognitive domains. For both SET-Intention Attribution and SET-Emotion Attribution, PDD showed a worse performance compared to PD-MCI, PD-NC and HC, while PD-MCI had significantly lower scores only compared to HC. Regarding the FACE test, only PDD scored significantly lower than all other groups. Correlation analyses revealed a statistically significant positive association between SET and most cognitive domains within the combined group of PD-MCI and PDD. Instead, the FACE test exhibited a significant positive correlation with language abilities. In the same group, apathy was significantly inversely correlated with SET. Prevalence of socio-cognitive deficits is similar to the one reported in literature (i.e., 9% of PD-NC, 23% of PD-MCI, and 75% of PDD for FER, and 19% of PD-MCI and 88% of PDD for ToM). Conclusions: PD showed a heterogeneous profile of cognitive impairments, characterized by deficits in each of the domains assessed. The PDD group was the most severely affected in every domain. Concerning SC abilities, PD-NC performed as controls, PD-MCI patients had significantly worse ToM abilities than HC, while PDD exhibited the most pronounced deficits in both ToM and FER tests. Cognitive and affective ToM seem to decline simultaneously from the early to moderate disease stages, and to deteriorate further as the disease progresses. Moreover, positive correlations were observed between ToM and the majority of cognitive domains only in the combined PD-MCI and PDD group, indicating that SC impairments might depend on the failure of “supporting” cognitive functions. Instead, FER was impaired only in PDD compared to the other groups, suggesting that PD-NC and PD-MCI might rely on compensatory mechanisms—such as recruitment of somatosensory areas and embodied simulation of emotions— to foster emotion recognition. Alternatively, since FER was associated with a worse performance in language abilities, its sparing in PD-NC and PD-MCI may be attributed to the cognitive load placed on the involved language domain not being high enough to produce significant deficits. Depression and anxiety did not contribute to SC impairments, while an intriguing negative correlation emerged between apathy and ToM only for PD-MCI and PDD patients, suggestive of an “executive” apathy subtype.