Introduction:
While identifying Alzheimer’s Disease (AD) in its early stages is crucial,
traditional neuropsychological tests tend to lack sensitivity and specificity for its diagnosis. Neuropsychological
studies have reported visual processing deficits of AD, and event-related potentials (ERPs)
are suitable to investigate pre-attentive processing with superior temporal resolution.
Objective:
This study aimed to investigate visual attentional characteristics of adults with AD, from
pre-attentive to attentive processing, using a visual oddball task and ERPs.
Methods:
Cognitively normal elderly controls (CN) and patients with probable AD (AD) were recruited.
Participants performed a three-stimulus visual oddball task and were asked to press a designated
button in response to the target stimuli. The amplitudes of 4 ERPs were analyzed. Mismatchnegativity
(vMMN) was analyzed around the parieto-occipital and temporo-occipital regions. P3a was
analyzed around the fronto-central regions, whereas P3b was analyzed around the centro-parietal
regions.
Results:
Late vMMN amplitudes of the AD group were significantly smaller than those of the CN
group, while early vMMN amplitudes were comparable. Compared to the CN group, P3a amplitudes of
the AD group were significantly smaller for the infrequent deviant stimuli, but the amplitudes for the
standard stimuli were comparable. Lastly, the AD group had significantly smaller P3b amplitudes for
the target stimuli compared to the CN group.
Conclusion:
Our findings imply that AD patients exhibit pre-attentive visual processing deficits,
known to affect later higher-order brain functions. In a clinical setting, the visual oddball paradigm
could be used to provide helpful diagnostic information since pre-attentive ERPs can be induced by
passive exposure to infrequent stimuli.
Atrophy of medial temporal lobes on MRI in "probable" Alzheimer's disease and normal ageing: diagnostic value and neuropsychological correlates.
