Brain activity during attention tasks in LBD and Alzheimer's
Alzheimer's disease and Lewy body dementia show distinct patterns of default mode network deactivation during attentional tasks despite similar behavioral deficits.
Source
Neural correlates of attention-executive dysfunction in lewy body dementia and Alzheimer's disease
Study at a glance
- Design
- Case-control — fMRI attention network test in LBD (DLB+PDD), Alzheimer's disease, and healthy controls
- N
- N=78 · 32 LBD, 23 AD, and 23 healthy controls in the fMRI analysis; ages >60, MMSE >12 for patients
- Population
- Community-dwelling older adults with mild-to-moderate LBD or Alzheimer's disease, and healthy controls
- Outcome
- Frontoparietal activation and default-mode deactivation during alerting, orienting, and executive attention
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Brain activity during attention tasks in LBD and Alzheimer's
These passages occur verbatim in the stored paper text. They support the points listed below; they do not verify every statement in the explanation.
23 healthy controls completed the protocol
There were 23 controls, 30 Alzheimer's disease, 24 dementia with Lewy bodies, and 22 Parkinson's disease with dementia subjects who completed the protocol.
23 participants with Alzheimer's disease were included in the final fMRI analysis
This left 23 controls (21 with six runs and 2 with five runs of fMRI data), 23 Alzheimer's disease (15 with six runs, 1 with five runs, and 7 with four runs of fMRI data), 19 dementia with Lewy bodies (12 with six runs, 4 with five runs, and 3 with four runs of fMRI Data), and 13 Parkinson's disease with dementia (12 with six runs, 1 with five runs).
What they did
The researchers scanned 23 healthy older controls, 23 participants with Alzheimer's disease, and 32 participants with Lewy body dementia while they completed a modified Attention Network Test. This test evaluated how participants responded to visual cues and resolved conflict when identifying the direction of arrow targets under different levels of difficulty.
What they found
Both dementia groups showed slowed reaction times and worse accuracy compared to controls, but did not differ from each other behaviorally. Neuroimaging showed that while both dementia groups activated normal frontoparietal networks, only the Lewy body dementia group showed healthy-like deactivation of the default mode network during the executive control task, whereas the Alzheimer's disease group failed to deactivate this network.
The limits
What it doesn't show
Because the study utilized visual stimuli, the findings might be confounded by visual-perceptual deficits common in Lewy body dementia. The potential influence of concurrent medications, such as cholinesterase inhibitors or dopaminergic treatments, could not be completely ruled out. Additionally, the analysis was restricted to regional cortical activity and did not map subcortical pathways or measure underlying amyloid pathology directly.
Key terms
- Lewy body dementia (LBD)
- A clinical term encompassing both dementia with Lewy bodies and Parkinson's disease dementia, marked by protein deposits in brain cells that cause cognitive, motor, and visual symptoms.
- Attention Network Test (ANT)
- A cognitive test designed to measure the efficiency of three separate attention networks: alerting, orienting, and executive control.
- Default Mode Network (DMN)
- A network of interacting brain regions that is typically active when a person is resting and quiet, and becomes deactivated during active, goal-directed tasks.
- BOLD signal
- Blood-oxygen-level-dependent signal, an indirect measure of neural activity used in functional MRI to track changes in blood flow and oxygen levels.
- Executive control
- The cognitive process of managing, focusing, and allocating attention to resolve conflicts and make decisions during complex tasks.
- Task-positive network
- A set of brain regions, including the frontoparietal control network, that increase in activity when a person is engaged in an externally focused, demanding task.
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Quiz yourself
Which clinical conditions are grouped under the diagnostic umbrella of Lewy body dementia (LBD) in this study?
Common questions
Why did the researchers group dementia with Lewy bodies and Parkinson's disease dementia together?
They combined them into a single LBD group because both diseases show highly similar attentional and cognitive profiles, and statistical tests on the task showed no significant behavioral or neuroimaging differences between them.
What makes the 'modified' Attention Network Test different from the standard version?
The modified task introduced two levels of conflict (easy and hard incongruent trials) by varying the arrangement of flanking arrows, allowing the researchers to study executive processing and task difficulty in greater depth.
Why is default mode network deactivation important during cognitive tasks?
Deactivating the default mode network allows the brain to allocate neural resources effectively to the task-positive networks needed to focus and make accurate decisions.
Did the dementia patients recruit different brain regions to compensate for their deficits?
No, both dementia groups utilized the same general frontoparietal networks as healthy controls rather than recruiting additional regions, although they showed greater overall activity increases with high task difficulty.
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