Article

Remembering the location of objects in the environment is both important in
everyday life and difficult for patients with amnestic mild cognitive impairment
(aMCI), a clinical precursor to Alzheimer's disease. To test the hypothesis that
memory impairment for object location in aMCI reflects hippocampal dysfunction,
we used an event-related functional magnetic resonance imaging paradigm to
compare patients with aMCI and healthy elderly controls (HEC) as they encoded 90
ecologically relevant object-location associations (OLAs). Two additional OLAs,
repeated a total of 45 times, served as control stimuli. Memory for these OLAs
was assessed following a 1-h delay. The groups were well matched on demographics
and brain volumetrics. Behaviorally, HEC remembered significantly more OLAs than
did aMCI patients. Activity differences were assessed by contrasting activation
for successfully encoded Novel stimuli vs. Repeated stimuli. The HEC demonstrated
activity within object-related (ventral visual stream), spatial location-related
(dorsal visual stream), and feature binding-related cortical regions (hippocampus
and other memory-related regions) as well as in frontal cortex and associated
subcortical structures. Activity in most of these regions correlated with memory
test performance. Although the aMCI patients demonstrated a similar activation
pattern, the HEC showed significantly greater activity within each of these
regions. Memory test performance in aMCI patients, in contrast to the HEC, was
correlated with activity in regions involved in sensorimotor processing. We
conclude that aMCI patients demonstrate widespread cerebral dysfunction, not
limited to the hippocampus, and rely on encoding-related mechanisms that differ
substantially from healthy individuals.
CI - Published by Elsevier Ltd.

Langue : ANGLAIS