Memory Phenotypes In Early, De Novo Parkinson's Disease Patients with Mild Cognitive Impairment

Dopaminergic Treatment and Episodic Memory in Parkinson's Disease: A Meta-analysis of the Literature

To date, few studies have focused on the benefits of dopaminergic treatment on episodic memory functions in patients affected by Parkinson's disease (PD). We conducted a meta-analysis to determine the effects of pharmacological therapy with dopamine in alleviating episodic memory deficits in Parkinson's patients. A secondary aim was to evaluate the role of dopamine in episodic memory circuits and thus in different memory systems. We conducted a comprehensive literature search in PubMed (1971-2022) to find studies that met specific inclusion criteria. The studies had to provide sufficient data (means and standard deviations) to evaluate performance on neuropsychological tests of episodic memory. A total of k = 36 measures were included in the analysis. A statistically significant difference suggested better performance following dopaminergic therapy assumption (ON condition) than following dopaminergic withdrawal (OFF condition), specifically the estimated pooled effect calculated through a random-effects restricted maximum likelihood model was log ratio of means (RoM) = 0.047 (p = 0.011). The back-transformed RoM, indicating a 4.8% improvement, provides an interpretable measure of the effect size, as it reflects the multiplicative change in performance associated with the ON condition. A meta-regression analysis was also performed to assess the influence of specific memory tasks and relevant covariates/factors on the overall meta-analytic effect: four memory contrasts (verbal/visual, immediate/delayed, recall/recognition, word-list/short-story), age of participants, years of education, severity of illness, duration of illness in years, country of study, proportion of women in the sample, type of medication, counterbalancing. Word list/short story and proportion of women in the sample were the only two statistically significant predictors in the model, both associated with a positive higher pooled effect size. The present study revealed a significant overall difference between the results obtained in the ON and OFF conditions. We also found a significantly greater pharmacological effect in the recall of short stories than word lists, which supports the hypothesis of a beneficial effect of dopamine on the hippocampal circuit rather than on prefrontal cortical areas.

Trends and hotspots in non-motor symptoms of Parkinson's disease: a 10-year bibliometric analysis

Non-motor symptoms are prevalent among individuals with Parkinson's disease (PD) and seriously affect patient quality of life, even more so than motor symptoms. In the past decade, an increasing number of studies have investigated non-motor symptoms in PD. The present study aimed to comprehensively analyze the global literature, trends, and hotspots of research investigating non-motor symptoms in PD through bibliometric methods. Studies addressing non-motor symptoms in the Web of Science Core Collection (WoSCC), published between January 2013 and December 2022, were retrieved. Bibliometric methods, including the R package "Bibliometrix," VOS viewer, and CiteSpace software, were used to investigate and visualize parameters, including yearly publications, country/region, institution, and authors, to collate and quantify information. Analysis of keywords and co-cited references explored trends and hotspots. There was a significant increase in the number of publications addressing the non-motor symptoms of PD, with a total of 3,521 articles retrieved. The United States was ranked first in terms of publications (n = 763) and citations (n = 11,269), maintaining its leadership position among all countries. King's College London (United Kingdom) was the most active institution among all publications (n = 133) and K Ray Chaudhuri was the author with the most publications (n = 131). Parkinsonism & Related Disorders published the most articles, while Movement Disorders was the most cited journal. Reference explosions have shown that early diagnosis, biomarkers, novel magnetic resonance imaging techniques, and deep brain stimulation have become research "hotspots" in recent years. Keyword clustering revealed that alpha-synuclein is the largest cluster for PD. The keyword heatmap revealed that non-motor symptoms appeared most frequently (n = 1,104), followed by quality of life (n = 502), dementia (n = 403), and depression (n = 397). Results of the present study provide an objective, comprehensive, and systematic analysis of these publications, and identifies trends and "hot" developments in this field of research. This work will inform investigators worldwide to help them conduct further research and develop new therapies.

Pathobiology of Cognitive Impairment in Parkinson Disease: Challenges and Outlooks

Cognitive impairment (CI) is a characteristic non-motor feature of Parkinson disease (PD) that poses a severe burden on the patients and caregivers, yet relatively little is known about its pathobiology. Cognitive deficits are evident throughout the course of PD, with around 25% of subtle cognitive decline and mild CI (MCI) at the time of diagnosis and up to 83% of patients developing dementia after 20 years. The heterogeneity of cognitive phenotypes suggests that a common neuropathological process, characterized by progressive degeneration of the dopaminergic striatonigral system and of many other neuronal systems, results not only in structural deficits but also extensive changes of functional neuronal network activities and neurotransmitter dysfunctions. Modern neuroimaging studies revealed multilocular cortical and subcortical atrophies and alterations in intrinsic neuronal connectivities. The decreased functional connectivity (FC) of the default mode network (DMN) in the bilateral prefrontal cortex is affected already before the development of clinical CI and in the absence of structural changes. Longitudinal cognitive decline is associated with frontostriatal and limbic affections, white matter microlesions and changes between multiple functional neuronal networks, including thalamo-insular, frontoparietal and attention networks, the cholinergic forebrain and the noradrenergic system. Superimposed Alzheimer-related (and other concomitant) pathologies due to interactions between α-synuclein, tau-protein and β-amyloid contribute to dementia pathogenesis in both PD and dementia with Lewy bodies (DLB). To further elucidate the interaction of the pathomechanisms responsible for CI in PD, well-designed longitudinal clinico-pathological studies are warranted that are supported by fluid and sophisticated imaging biomarkers as a basis for better early diagnosis and future disease-modifying therapies.