Domain-driven verbal and non-verbal dissociations in cognition and social cognition in Parkinson's disease

Beyond motor symptoms, Parkinson's disease (PD) affects cognition and social cognition. This is already evident in cognitively intact PD, but is especially prominent in those with mild cognitive impairment (PD-MCI). The impact of processing modality (verbal vs. non-verbal) remains unclear. We examined differences across verbal and non-verbal components of cognition and Theory of Mind (ToM) in subjects with PD or PD-MCI compared to healthy controls (HC).

Seventy-seven participants (HC = 26; PD = 28; PD-MCI = 23) completed a battery of neuropsychological tests to assess verbal and non-verbal cognition, verbal and non-verbal ToM. Data were analyzed using non-parametric statistics and multinomial logistic regression models.

Both PD groups showed statistically significant impairments compared to HC, with more pronounced deficits in PD-MCI. Verbal cognition was reduced in both PD groups (HC = 3.55 ± 0.59; PD = 2.76 ± 0.95; PD-MCI = 2.73 ± 0.95; χ² = 27.46, p < 0.001, η² = 0.34), while non-verbal cognition was only affected in PD-MCI (HC = 3.54 ± 1.92; PD-MCI = 2.59 ± 1.40; χ² = 16.17, p < 0.001, η² = 0.19). Verbal ToM was selectively impaired in PD-MCI (HC = 6.27 ± 1.00; PD-MCI = 4.94 ± 1.95; χ² = 9.07, p = 0.01, η² = 0.10), while non-verbal ToM was substantially preserved (p > 0.33). The regression analysis confirmed that lower scores in verbal and non-verbal cognition were associated with a higher likelihood of PD-MCI classification.

The pattern emerging from our findings is consistent with a framework in which domain-specific vulnerabilities are primary, while modality may influence performance in interaction with task complexity and executive demand. This 2 × 2 framework (domain X modality) refines our understanding of cognitive decline in PD and underscores the need for domain- and modality-sensitive assessments.