Patients with amnestic mild cognitive impairment (aMCI) often display deficits in episodic memory. Amnestic
MCI is now recognized as a prodromal form of Alzheimer's disease. Various aMCI clinical subtypes have been identified
as ingle-domain (SD) or multi-domain (MD). The various subtypes represent heterogeneous syndrome indicating the
probability of progression to AD, impaired cognitive domains and so on. To examine the characteristics of brain regions
of aMCI subtypes is likely to be important for early diagnosis and prediction to AD. This study investigated brain functional
activation and hippocampal atrophy during a visually complex scene encoding in 20 individuals with aMCI-SD, 14
individuals with aMCI-MD and 25 healthy controls. During the encoding task, aMCI-MD patients had reduced activation
in right superior medial frontal, right inferior and middle temporal, right middle occipital and left inferior frontal regions
compared to controls. The different active brain regions between aMCI-MD and aMCI-SD patients are the right middle
occipital and left middle cingulum regions. The aMCI-MD group had significantly lower left hippocampus volumes compared
to the aMCI-SD group and controls, but there was no difference between aMCI-SD patients and the control group in
terms of left hippocampus atrophy. The findings provide evidence that aMCI may represent a heterogeneous group. The
aMCI-MD patients displayed more severe hippocampcal atrophy and fMRI activation changes than aMCI-SD. The aMCIMD
may represent a more advanced prodromal stage of AD.
Keywords: Alzheimer's disease, amnestic mild cognitive impairment, episodic memory, fMRI, hippocampus.
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