Objectives Delusional thoughts are common among patients with Alzheimer’s disease (AD) and may be conceptually linked to memory deficits (cannot recall accurate information which fosters inaccurate beliefs) and poor insight (unable to appreciate the illogic of beliefs). This study’s goals were to examine the clinical associations among delusions, memory deficits, and poor insight, explore neurobiological correlates for these symptoms, and identify shared mechanisms. Design Cross sectional analysis. Setting VA Greater Los Angeles Healthcare System. Participants Eighty-eight outpatients with AD (mean MMSE 19.3). Measurements Delusional thoughts were assessed with the Neuropsychiatric Inventory. Level of inaccurate insight was assessed with the Neurobehavioral Rating Scale (NRS). Memory was assessed with the Mattis Dementia Rating Scale (DRS) memory subscale. 18F-FDG PET imaging was used to measure regional cortical metabolism. Relationships between clinical ratings and regional cortical metabolic activity (voxel-based) were assessed using SPM2. Results Patients with delusions had lower DRS memory subscale scores. NRS inaccurate insight scores were no different in those with and without delusions. Cortical metabolic activity was lower in the right lateral frontal cortex, orbitofrontal cortex, and bilateral temporal cortex in patients with delusions. Low cortical metabolic activity in the right lateral, inferior, and medial temporal cortex was associated with poorer memory. This region partially overlapped the region of hypometabolism associated with delusions. In contrast, low cortical metabolic activity in bilateral medial frontal cortex was associated with poor insight. Conclusions Delusions in AD are associated with dysfunction in specific frontal and temporal cortical regions. Delusions are partially clinically and neurobiologically linked to memory deficits but not to poor insight.

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