Is verbal episodic memory in elderly with amyloid deposits preserved through altered neuronal function?

Area of Science:

• Neuroscience
• Gerontology
• Medical Imaging

Background:

• Cognitively normal elderly individuals can harbor beta-amyloid (Aβ) pathology, a hallmark of Alzheimer's disease (AD).
• Heightened cerebral glucose metabolism is a proposed mechanism for intellectual preservation in this population.
• Understanding the interplay between Aβ, metabolism, and cognition is crucial for early AD detection and intervention.

Purpose of the Study:

• To investigate the cross-sectional relationships between Aβ deposition, cerebral glucose metabolism, and cognitive performance in cognitively normal elderly subjects.
• To explore whether heightened glucose metabolism acts as a compensatory mechanism for cognitive preservation in the presence of Aβ pathology.

Main Methods:

• 81 cognitively normal elderly subjects (mean age 75 ± 7 years) underwent [(11)C]Pittsburgh Compound-B (PIB) and [(18)F]fluorodeoxyglucose (FDG) positron emission tomography (PET) scans.
• Subjects were categorized into low, intermediate, and high Aβ groups based on global cortical PIB retention.
• Cognitive function was assessed using validated neuropsychological tests measuring episodic memory, semantic memory, working memory, and executive functioning.

Main Results:

• Greater Aβ deposition in the precuneus was associated with a trend towards higher metabolic activity and lower visual episodic memory scores.
• No overall correlation between glucose metabolism and cognition was found across all subjects.
• In subjects with elevated amyloid levels, heightened metabolic activity was significantly associated with better verbal episodic memory performance.

Conclusions:

• Neural compensation, potentially reflecting brain reserve, may enable elderly individuals with preclinical AD pathology to temporarily maintain cognitive function.
• Heightened cerebral glucose metabolism appears to be a compensatory mechanism supporting specific cognitive domains, particularly verbal episodic memory, in the presence of amyloid.
• This preliminary study highlights the dynamic interplay between Aβ, brain metabolism, and cognitive resilience in aging.