Beta-amyloid deposition, a hallmark of Alzheimer's disease, is also common in cognitively normal older adults. Using Pittsburgh compound-B PET imaging, the study found that greater beta-amyloid burden in normal controls is associated with altered functional connectivity within the default mode network during rest. Connectivity decreased in regions critical for episodic memory, including posteromedial cortex, ventral medial prefrontal cortex, and angular gyrus, while increases appeared in dorsal and anterior medial prefrontal and lateral temporal cortices. The decreases align with known vulnerability of memory-related areas in Alzheimer's disease, and the increases may reflect compensatory mechanisms.
Psychosis is a common and burdensome symptom in neurodegenerative diseases. Analyzing 283 autopsy-confirmed cases, delusions were linked to atrophy in the right temporal lobe and bilateral frontal lobes, especially when persecutory or paranoid, implicating circuits for reward, emotion, self-awareness, and executive function. Misidentification delusions correlated with right ventral temporal-occipital atrophy, disrupting visual stream processing. No consistent atrophy patterns emerged with hallucinations. Damage to these brain regions predisposes individuals to delusions across different syndromes and pathologies, suggesting shared mechanisms between neurologic and psychiatric disorders.