Visual processing capacity and cognitive decline in Parkinson's disease

Abstract

Background: Parkinson's disease (PD) is a progressive neurodegenerative disorder characterised by motor symptoms. However, approximately half of patients with PD exhibit signs of dementia within a decade of diagnosis. While deficits in working memory and visuospatial abilities are recognised as hallmarks of cognitive decline in PD, these populations are rarely studied using detailed cognitive tools that link cognitive impairments to formal theoretical models, such as the theory of visual attention (TVA).

Methods: This cross-sectional study addresses this gap by employing the TVA whole report paradigm to assess visual processing in a cohort of patients with PD, both with and without cognitive impairment. Participants were divided based on their Montreal Cognitive Assessment (MoCA) scores into two PD groups (n=25 each) and a healthy control group (n=25).

Results: Our principal finding is that the visual processing speed (C) and visual short-term memory capacity (K) are significantly diminished in patients with PD with MoCA scores below 26 (Analysis of variance, p=0.016 for C and p<0.001 for K), while no notable differences were observed between controls and patients with PD with MoCA scores of 26 or above. Using a generalised linear model to assess the impact of factors such as age, gender and disease duration, we discovered that the C-parameter was significantly influenced by age, while the K-parameter was notably affected by gender.

Conclusion: TVA parameters demonstrate their suitability for detecting cognitive deficits in PD. Given their independence from motor and non-motor symptoms, TVA parameters may prove to be valuable tools for early diagnosis and longitudinal monitoring of cognitive deficits in individual patients with PD.

Keywords: COGNITION; PARKINSON'S DISEASE; VISUAL ATTENTION.

Figure 1. Whole report paradigm: example for one trial. The fixation point initiates the trial, followed by a stimulus display. In the whole report, the stimulus at display consists of six letters and all of them are either red or blue. After the stimulus, in most trials, a pattern mask is presented. The only exceptions to this are two trial conditions where no masking is applied. Finally, the participant reports the recognised stimuli verbally. Figure created with Biorender.com

Figure 2. Boxplots of fitted TVA parameters. Groups: HC, healthy controls; PD-ND, patients with PD with MoCA≥26; PD-CD, patients with PD with MoCA≤25. *Significant group differences in t-test for independent groups, differences are considered significant a p≤0.05. MoCA, Montreal Cognitive Assessment; TVA, theory of visual attention; VSTM, visual short-term memory.

Figure 3. Correlation matrix of TVA parameters and PD-specific clinical scores (N = 50). Pairwise correlations (Pearson’s correlation) between clinical markers, scores and TVA parameters, with non-significant correlations marked by an X. Values are considered significant at p≤0.05, after correction for multiple comparisons using the false discovery rate (FDR) method. The intensity of the correlation coefficient is depicted by colour, with red for 1 and blue for −1. MoCA, Montreal Cognitive Assessment; PD, Parkinson’s disease; QUIP-RS, Questionnaire for Impulsive-Compulsive Disorders in PD Rating Scale; NMS-Quest, non-motor Symptoms Questionnaire; PDQ-8, Parkinson’s disease Questionnaire 8; TVA, theory of visual attention; UPDRS, Unified Parkinson’s Disease Rating Scale; VSTM, visual short-term memory.