The cause of Alzheimer's disease, the most common form of dementia, remains unknown. Neuropathological studies suggest that a small area in the brainstem, the locus coeruleus, might be the site of the onset of the disease. This area is the sole source of noradrenalin to the brain, a neurotransmitter involved in arousal, but also cognitive functions. Animal and pharmacological studies have hinted towards an important role of this area in memory functioning. However, these studies were hampered by the limited spatial resolution, making it hard to clearly localize the locus coeruleus in the brain. New developments in brain imaging allow now to visualize the brain with stunning precision. Furthermore, a non-invasive new stimulation method, transcutaneous vagus nerve stimulation, is believed to excite the locus coeruleus and thereby influencing neuronal networks and memory functioning. There are three aims in this project: 1. To investigate how the functional interaction between the locus coeruleus and other brain areas, in particular the medial temporal lobe areas, during memory processes (encoding, consolidation and retrieval) change with development of Alzheimer's disease. 2. To investigate associations between noradrenaline, memory performance and brain functioning. The investigators aim to investigate how acute noradrenalin levels change during the different memory processes and whether or not this is beneficial for performance. Furthermore, the investigators will investigate whether this interaction between noradrenalin, memory performance and brain functioning is different healthy older individuals (n =35) or patients with prodromal Alzheimer's disease (n =35). 3. To investigate the underlying neural network changes during transcutaneous vagus nerve stimulation. The investigators will focus on differences in functional connectivity between the locus coeruleus and the medial temporal lobe areas in healthy older individuals and prodromal Alzheimer's disease patients. An experimental condition will be compared with a sham condition in a pseudo-randomized cross-over design.
Study Type
OBSERVATIONAL
Enrollment
70
This is not an intervention, we investigate the neural mechanisms
Maastricht University
Maastricht, Netherlands
RECRUITINGBlood Oxygen Level Dependent (BOLD) response during a memory task
BOLD response contrasts during encoding and retrieval. For encoding: comparing neutral versus emotional, comparing old versus prodromal AD and the interaction emotional level by group. For retrieval: correctly remembered versus those incorrectly remembered; neutral versus emotional faces; lures, mistakes and hits. These contrasts will be investigated comparing both groups. BOLD responses during the memory task will also be compared across sessions (sham versus stimulation) for both groups. Consolidation: task-free, so the BOLD response in the locus coeruleus will be correlated with the BOLD response in any other voxel of the grey matter of the brain over time (seed-based resting-state analyses).
Time frame: 60 minutes
Performance on the memory task
Mean reaction times and accuracy levels during encoding and retrieval for emotional and neutral face-name associations and for old and prodromal AD patients. Mean reaction times and accuracy levels will also be compared across sessions: sham versus stimulation for both groups Mean reaction times and accuracy levels will also be correlated with BOLD responses during the memory task.
Time frame: 60 minutes
Noradrenalin levels during the memory task
Noradrenalin levels will be measured 7 times: double baseline, before encoding, after encoding, before retrieval, after retrieval and follow-up. Noradrenalin levels will be correlated with BOLD responses during the memory task.
Time frame: 60 minutes
Grey matter volume of the locus coeruleus
manual measurement of the number of voxels of the locus coeruleus: to compare groups
Time frame: 5 mintues
shape properties of the locus coeruleus
Correspondence of the location between triangle meshes (shape of the locus coeruleus) will be compared between groups
Time frame: 5 minutes
Performance on neuropsychological tests
Total score on the mini-mental state examination, fluency test, letter-digit-substitution test, concept shifting task, stroop color word test and the word learning task will be compared across groups. For the stroop color word task and the concept shifting task we will also compare reaction times between both groups. These scores will be correlated to the grey matter volume of the locus coeruleus and the shape properties of the locus coeruleus.
Time frame: 30 minutes
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