The Alzheimer disease (AD) is characterized because it begins to develop long before the affected person begins to manifest the first symptoms, such as memory loss and confusion or behavioral changes, and now it has been discovered that its presence can be detect early thanks to ‘brain fingerprints’ or subtle differences in brain function of older adults who appear when this type of dementia is in the preclinical phase.
The finding is the result of research carried out by neuroscientists at the Medical University of South Carolina (MUSC), who have designed individualized maps of brain function thanks to a new brain imaging analysis technique, which have allowed them to see if there were links between the subtle changes in brain function and the reduced cognitive performance which has been assessed through behavior-based tests.
This method could improve the study of the preclinical phase of Alzheimer’s, which could help to understand how the disease starts and progresses. “Previous studies have not found an association between brain function and behavior in preclinical AD,” said Andreana Benítez, who co-led the study. “Using these individualized maps of brain function, we found a potential brain-based reason for very subtle cognitive changes at this early stage of the disease.”
Subtle Changes in Brain Function Early in Alzheimer’s
The researchers looked at brain activity using a type of brain map called a functional connectome, which measures how different regions of the brain communicate with each other. Stephanie Fountain-Zaragoza, who has also directed the work, explains that it is as if the brain were a city and its regions were grouped into neighborhoods connected by highways. With the functional connectome, you look at the activity in that city: what happens in each neighborhood and how traffic flows between them.
Certain changes in the brain’s fingerprint were linked to worse information processing in people with beta-amyloid accumulations or preclinical Alzheimer’s disease.
For the new study, however, they used an individualized functional connectome developed by a collaborator, Hesheng Liu, which enabled them to carry out a novel and highly sensitive form of image analysis to appreciate how these neighborhoods function in people. So while traditional functional connectomes use an average of many people’s brains as a map for functional brain regions, the method created by Liu can show the unique patterns of each individual’s brain function.
“We all have the same functional parts of our brain, but they are positioned slightly differently, like a kind of fingerprint”, pointed out Fountain-Zaragoza. “This method creates an individualized brain fingerprint that more accurately reflects where different functional regions are located in each individual’s brain.”
Using this novel brain fingerprinting technique, the researchers looked for subtle changes in brain function in 149 individuals between the ages of 45 and 85 who showed no signs of cognitive decline. Brain PET scans were performed on all of them and they were divided into two groups depending on whether the test results showed evidence of early accumulation of beta-amyloid proteinor not, and they were also subjected to magnetic resonance imaging that served to generate the fingerprints of the brain.
These scientists then tested how each of the two groups performed behavior-based information processing tests and found that certain changes in the brain’s fingerprint were associated with worse information processing in those participants who they had amyloid beta accumulations or preclinical Alzheimer’s disease.
In participants with preclinical Alzheimer’s, information processing was worse in those with higher-than-usual inter-network connectivity or excessive activity on the brain’s highways. In contrast, information processing was better in those with greater connectivity within the network or more brain activity in important ‘neighborhoods’ of the brain.
“A healthy brain normally has a balance of connectivity within and between its networks,” said Fountain-Zaragoza. “We found that, in preclinical AD, when amyloid accumulation is present in the brain, this balance can be disturbed, which can lead to the information is no longer processed as efficiently”.
The results of the study have been published in Brain Connectivity and reveal that individualized functional connectomes are capable of detecting subtle variations in brain function that might be missed using conventional brain imaging techniques, and suggest that early phases of beta-amyloid accumulation could affect the function of amyloid-beta cells. brain networks and changes in their connectivity even before the symptoms of cognitive impairment are appreciated, so this imbalance in connectivity could be a good target to direct the therapies of Alzheimer’s patients.