Delusions and Cognitive Functioning in Alzheimer's Disease

Claire Milgrom, Fielding's School of Psychology

Alzheimer’s disease (AD) is a neurodegenerative disease of unknown etiology that affects cognitive functioning and functioning of daily living, and is frequently accompanied by behavioural and psychological symptoms (BPSD) including delusions, hallucinations, apathy, agitation, aggression, and depression. The presence of delusions in dementia patients is generally thought to be indicative of more advanced cognitive decline. Delusional thinking in people with dementia has also been found to be associated with aggressive behaviour, increased caregiver burden, high rates of institutionalization, and significant morbidity. Using data from the Alzheimer’s Disease Neuroimaging Initiative (ADNI), this study focused on the relationship between delusions in individuals with AD, their impairment in global and specific neuropsychological functioning (e.g., memory, executive functioning), and their functioning in daily living. It compared the neuropsychological functioning and daily functioning of AD patients with and without delusions. It also examined if the presence of delusions was associated with greater decline over time in global functioning, in specific cognitive domains, and in activities of daily living for patients with AD.

The results showed that delusions in AD patients may be more associated with the stage and progression of the illness rather than overall cognitive functioning or any specific neurocognitive indices. The results also indicated greater decline in daily functioning over time for AD patients who experienced delusions when compared to those who did not. This is an important finding in terms of its clinical application to assessment and intervention with AD patients.

Central to this study was the theoretical explanation of delusions using deficit or defect models. These models view delusions as “disorders of belief,” that is, “disruptions or alterations in the normal functioning of belief mechanisms such that individuals come to hold erroneous beliefs with remarkable tenacity” (McKay, Langdon & Coltheart, 2007, p. 933). A deficit model explains delusions as the result of fundamental cognitive or perceptual abnormalities stemming from disturbances in neurobiologically based cognitive-perceptual apparatus, distorted cognitive processes, or both.