Objective: To identify the neural substrates of Parkinson’s disease dementia (PDD) and Parkinson’s disease with Mild Cognitive Impairment (PD-MCI) using a network mapping approach.

Background: Dementia is a common and devastating symptom of PD but the anatomical substrates are still not clear. Neuroimaging abnormalities in PDD have been reported throughout the brain and are largely inconsistent across studies. Here we test whether heterogeneous findings for PDD localise to a specific brain network by using a new approach: coordinate-based network mapping.

Method: We used a literature search to identify studies reporting neuroimaging correlates of PDD (n=11). We restricted our search to studies of brain atrophy and hypometabolism that compared PD dementia to those without cognitive involvement.  We used a standard coordinate-based ALE meta-analysis to examine consistency in neuroimaging findings.  We then used coordinate-based network mapping to test whether neuroimaging findings localize to a common brain network.  This uses resting state functional connectivity from a large cohort of normal subjects (n=1000) to identify the network of regions connected to reported neuroimaging coordinates.

Results: The standard ALE meta-analysis did not identify brain regions associated with PDD.  In contrast, our new approach showed that heterogeneous neuroimaging findings localize to a network centred on the hippocampus.  Next we tested for stage specificity by using studies of PD-MCI (n=15).  Coordinate-based network mapping revealed that correlates of PD-MCI fell within a network centred on the posterior default mode network.

Conclusion: Our results link heterogeneous neuroimaging findings in PDD to a common network centred on the hippocampus, pointing to a central role for the hippocampi in established PD dementia.  In contrast, our finding that posterior brain networks are involved in PD-MCI sheds light onto the earlier stages of PDD. This has implications for understanding the progression of dementia in PD and for testable hypotheses regarding therapeutic targets.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/neuroimaging-in-parkinsons-disease-dementia-connecting-the-dots/