Clinical Manifestations.

Area of Science:

• Neuroscience
• Cognitive Psychology
• Gerontology

Background:

• Response time (RT) is traditionally linked to processing speed but may also reflect memory consolidation.
• Alzheimer's disease (AD) pathology disrupts hippocampal-cortical networks, potentially impacting memory retrieval before overt cognitive decline.
• This study investigates how memory recall RT changes with learning and its association with brain amyloid and tau burden.

Purpose of the Study:

• To examine the evolution of memory recall RT across repeated learning sessions.
• To determine the correlation between memory recall RT and brain amyloid and tau pathology.
• To explore age-specific associations between RT and AD biomarkers.

Main Methods:

• 175 cognitively unimpaired older adults completed daily associative memory tests over seven days.
• Memory consolidation was assessed by comparing RT and accuracy correlations between early (Day 1) and late (Days 5-7) phases.
• In a subsample (n=150), late-consolidation RT was regressed on amyloid and tau PET imaging, with age-specific analyses conducted.

Main Results:

• Recall RT significantly shortened from Day 1 to Days 5-7, indicating improved recall efficiency.
• The correlation between RT and accuracy strengthened over time, supporting RT as a measure of memory consolidation.
• Slower late-consolidation RT was associated with higher medial temporal tau, but not with neocortical tau or amyloid.
• An age-specific effect showed neocortical tau impacting RT in individuals under 74, while age alone influenced RT in those 74 and older.

Conclusions:

• Recall RT, even for correct responses, tracks memory consolidation and serves as a pathology-specific marker.
• Tau burden, alongside age, influences RT, suggesting its potential for detecting early Alzheimer's disease pathology.
• RT offers a sensitive metric complementing accuracy measures, especially in preclinical stages of cognitive decline.