Semantic memory activation in amnestic mild cognitive impairment

Area of Science:

• Neuroimaging
• Cognitive Neuroscience
• Alzheimer's Disease Research

Background:

• Cognitively intact older adults at risk for Alzheimer's disease (AD) often exhibit increased fMRI activation, presumed to be compensatory.
• Mild cognitive impairment (MCI) patients typically show reduced neural activation, linked to diminished neural reserve.
• Previous studies used memory tasks that disadvantaged MCI participants, potentially masking compensatory mechanisms.

Purpose of the Study:

• To investigate if increased brain activation is preserved in amnestic MCI using a controlled semantic memory task.
• To compare brain activation patterns in MCI, at-risk cognitively intact elders, and controls.

Main Methods:

• Event-related fMRI on 57 participants (19 each: MCI, At Risk, Control) aged 65-85.
• A low-effort, high-accuracy famous name discrimination task was used.
• Neuropsychological testing and MRI for atrophy assessment were performed.

Main Results:

• No group differences in demographics or task performance (>87% accuracy).
• MCI and At Risk groups showed greater activation than Controls in semantic memory regions.
• MCI patients exhibited increased hippocampal activation when hippocampal atrophy was accounted for.

Conclusions:

• When task performance is matched, MCI patients demonstrate compensatory functional activation in semantic memory circuits.
• This hyperactivation in MCI equals or exceeds that of cognitively intact individuals at risk for AD.
• Compensatory hyperactivation in MCI extends to the hippocampus, particularly when atrophy is controlled.