Fluid Intelligence in Parkinson’s Disease and Mild Cognitive Impairment

Introduction: Fluid intelligence (Gf) is the ability to perceive relationships between different stimuli and to derive associations. Gf involves many processes, including making inferences, creating hypotheses, and transforming information, that enable the use of diverse strategies to solve problems in novel contexts. This ability reaches its peak during adolescence and declines from early adulthood. This study aims to assess the Gf decline in healthy older individuals (HC) and different forms of pathological aging, such as Parkinson's disease (PD) and Mild Cognitive Impairment (MCI). Methods: Eighty-one participants were divided into three groups: 27 individuals diagnosed with MCI (mean age:69.1±7), 27 participants with PD (mean age:70.1±9.4), and 27 HC (mean age:69±8.4). Raven's Standard Progressive Matrices (RSPM) were used to assess Gf. Results: ANOVA showed significant differences in the RSPM (F=7.3, p<.001): individuals with PD exhibited a poorer performance (mean:28.5±12.1) than HC (mean:39.3±10.7, p=0.001) and individuals with MCI (mean:36.2±9.1, p=0.03), while there was no significant difference between participants with MCI and HC. Conclusions: The diminished Gf performance in the group with PD could be attributed to a greater brain disruption in this group compared to the others. Gf is associated with several areas, including basal ganglia, striatum, caudate, and their connections to the prefrontal cortex. Although the impairment of frontal networks in healthy aging and MCI is well-documented, these results suggest that these areas are more impaired in PD. In PD, the alterations of frontostriatal circuits are characterized by an imbalance of dopamine, which is involved in the development of cognitive symptoms, including poor Gf.