Associative encoding deficits in amnestic mild cognitive impairment: a volumetric and functional MRI study

Abstract

Background: Previous functional MRI studies have shown increased hippocampus activation in response to item encoding in amnestic mild cognitive impairment (aMCI). Recent behavioral studies suggested that associative memory could be more impaired than item memory in aMCI. So far, associative encoding has not been evaluated separately from item encoding in functional MRI studies.

Methods: We conducted a volumetric and functional MRI study investigating associative encoding in 16 aMCI and 16 elderly controls while controlling for item encoding.

Results: We confirmed the presence of associative memory impairment in aMCI even after controlling for item memory differences between groups. Associative memory but not item memory correlated with hippocampus volume in aMCI. Such a correlation was not observed in elderly controls. The left anterior hippocampus activation in response to successful associative encoding was decreased in aMCI, even after correction for hippocampus atrophy.

Conclusion: Associative memory impairment in aMCI appears to be related to hippocampus atrophy and left anterior hippocampus hypoactivation.