[Visual search in Alzheimer disease--an functional magnetic resonance imaging study].
OBJECTIVE
To investigate the functional activation patterns during two types of visual search tasks in Alzheimer's disease (AD) with functional MRI, and probe the neuro-anatomic basis of visual attention.


METHODS
13 patients with AD and 13 sex and age-matched healthy subjects participated in the experiment designed with two visual search tasks. The first was a "pop-out" single feature task, detecting a vertical target among horizontal distractors, and the second was a conjunction task where the target was defined by conjunction of feature (color and orientation) and the performance depended on some shifting of attention. The fMRI data were collected by Siemens 1.5 T Sonata magnetic resonance imaging (MRI) system and analyzed by Statistical Parametric Mapping software (SPM 99) to generate the activation map.


RESULTS
AD patients had a particular impairment in the conjunction task but not in the single-feature task. Although both groups revealed overlapping networks engaged in the conjunction tasks including the superior parietal lobule (SPL), frontal and occipitotemporal cortical regions (OTC), primary visual cortex and some subcortical structures, the most pronounced difference between them was found in bilateral SPL (more activities in the controls) and right OTC (more activities in the patients). The difference between the 2 groups was small in the pop-out condition.


CONCLUSIONS
AD particularly affects those mechanisms controlling spatial shifts of attention. Some additional remote activation (ventral visual stream and temporal lobe) can be interpreted as dynamic reallocating of brain functional resource.
Hao
Jing
J
Department of Radiology, Xuanwu Hospital, Capital University of Medical Sciences, Beijing 100053, China.
Li
Kun-cheng
KC
Wang
Wei
W
Yang
Yan-hui
YH
Li
Ke
K
Yan
Bin
B
Zhan
De-xuan
DX
D000368:Aged; D000544:Alzheimer Disease / Q000523:psychology*; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D011930:Reaction Time; D014796:Visual Perception