Date of Award

12-2024

Document Type

Thesis

Degree Name

Master of Arts in Psychological Science

Department

Psychology

First Reader/Committee Chair

Jones, Jacob

Abstract

In Parkinson’s Disease (PD), research has shifted to investigate how biomarkers commonly seen in Alzheimer’s Disease (AD), such as amyloid beta (AB), may be associated with cognitive functioning in PD. AB is considered a reliable biomarker for AD pathology, however in PD there is a lacking biomarker that can accurately reflect severity of cognitive impairment. AD research has shown an association between low AB and cognitive decline, but the data in PD has mixed results. Most studies that analyze cognitive decline and biomarkers do not use a cutoff level and the few that do have a threshold vary greatly in terms of the cutoff level. The purpose of this study was to determine if there were any cognitive differences between individuals who are amyloid positive in contrast to those that are amyloid negative. We also examined the association between amyloid beta levels and cognition amongst those individuals who are amyloid negative. This allowed us to determine if subclinical/threshold variability in amyloid was associated with cognition.

A secondary analysis using Parkinson’s Progression Marker’s Initiative (PPMI) data was run to analyze 929 newly diagnosed participants for longitudinally in both clinical and biological data including neuropsychiatric assessments, motor assessments, and cerebrospinal fluid yearly.

We used two thresholds to determine whether individuals are amyloid positive or negative; a/mL cut-off (Abildgaard et al., 2023) and a/mL cutoff (Shaw et al., 2018).

Multilevel modeling (MLM) was conducted to examine group differences (amyloid positive vs amyloid negative) in longitudinal trajectory of cognitive functioning. We examined the longitudinal association between CSF amyloid markers and cognitive functioning among a subsample of amyloid negative PD participants also using MLM analyses.

There were no significant group differences or group X time interactions in any cognition domains.

Currently there is no consensus on determining toxic levels of amyloid beta (AB). The use of cutoff levels may aid in early clinical diagnosis and provide a more reliable measure of neurodegeneration, however finding an adequate cutoff level proves to be a challenge for researchers.

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