Memory encoding in Alzheimer's disease: An fmri study of explicit and implicit memory
Alexandra J. Golby, Gerald Silverberg, Elizabeth Race, Susan Gabrieli, James P. O’Shea, Kyle Knierim, Glenn Stebbins, John Gabrieli
Alzheimer’s disease is the most common cause of dementia
in older adults. Although the cognitive deficits and pathologic
hallmarks of Alzheimer’s disease have been well
characterized, few functional imaging studies have examined
the functional competency of specific brain regions
and their relationship to specific behavioural memory deficits
in Alzheimer’s disease. We used functional MRI
(fMRI) to examine seven early stage Alzheimer’s disease
patients and seven healthy age-matched neurologically
normal control subjects during intentional encoding of
scenes. Subjects viewed blocks of novel scenes, repeated
scenes or baseline. Data were analysed using whole-brain
statistical parametric mapping and region of interest
approaches. The Alzheimer’s disease group demonstrated
impaired explicit recognition memory, but intact implicit
memory (repetition priming), for the scenes. Alzheimer’s
disease patients demonstrated a graded deficit in activation
for novel versus repeated scenes along the ventral visual
stream, with most impaired activation changes in the
mesial temporal lobe (MTL) and fusiform regions, most
preserved activations in primary visual cortex and
variably affected activations in secondary visual areas.
Group-level correlations with behavioural measures of
explicit memory were found in MTL, lingual and fusiform
areas, whereas correlations with priming were found in
lateral occipital, parietal and frontal areas. Together,
these fMRI findings indicate a dissociation in Alzheimer’s
disease between impaired explicit memory encoding in
MTL and fusiform regions and intact implicit encoding
in earlier-stage occipital cortex.
Group statistical activation maps for the novel > repeat contrast (threshold P < 0.001) for the Alzheimer’s disease (AD) and normal control (NC) subjects superimposed on averaged anatomical images for each group.
Memory encoding in Alzheimer's disease: An fmri study of explicit and implicit memory
Alexandra J. Golby, Gerald Silverberg, Elizabeth Race, Susan Gabrieli, James P. O’Shea, Kyle Knierim, Glenn Stebbins, John Gabrieli
Brain
2005; 128. 773-787.