A holistic analysis of relationships between executive function and memory in Parkinson's disease

Apart from motor symptoms, Parkinson's disease is characterized by executive and memory problems that have been observed from early stages of the disease. This study explores the possible relationships between these cognitive impairments in a group of 23 individuals with Parkinson's disease (PD) in comparison to a group of 18 healthy individuals. Compared with young individuals, normal aging is characterized by an increased association between executive function and episodic memory, especially with verbal material. We hypothesize that this association between verbal episodic memory and executive function may be weaker in PD as a consequence of the decline in these two cognitive abilities. To test this hypothesis, three categories of standardized tests were administered to both groups: (a) tests for executive function, (b) tests for visuospatial episodic memory, and (c) tests for verbal episodic memory. Performance outputs were analyzed using factor analysis, canonical regression, and structural equation modeling to obtain a holistic perspective of the linkage of these processes and to compare the differences between groups. In general, PD patients performed worse than controls in both executive function and episodic memory (with verbal and visuospatial material). Moreover, we found that relationships between executive function and visuospatial memory scores were high and quite similar in both groups. However, the relationship between verbal episodic memory and executive function was weaker in PD than in healthy individuals. These results suggest that a different brain mechanism could explain executive and verbal memory impairments in PD.