Background
Our brain contains thousands of connections that ensure optimal communication between various areas. This is very similar to how roads connect town regions and ensure communication between them. In a road analogy, some connections might be disrupted because of heavy traffic or because of an accident, which results in slower traffic on that route. In some disorders such as Alzheimer’s disease, we see a similar pattern of disrupted brain connections.
In the concept of brain connectivity, we distinguish between structural and functional connections. Any neighbouring brain regions are structurally connected. On the other hand, two or more brain regions are functionally connected when they are simultaneously active as a response to a particular stimulus, regardless of their structural connections. This results in formation of brain networks. For example, some regions are simultaneously active when we are at rest doing nothing, and this activity forms so-called resting-state networks.
By using brain imaging, previous research found that both structural connectivity and functional connectivity in patients with Alzheimer’s Disease differed from those in healthy individuals. Particularly, structural differences were observed in connections from and to brain areas related to memory and functional differences were observed in multiple resting-state networks.
Why is the study important?
Brain imaging tools can detect brain differences associated with dementia and can be used to predict which patients with cognitive impairment might progress to developing Alzheimer’s disease. However, the use of brain imaging to diagnose Alzheimer’s is currently limited to assessment of brain shrinkage, which is unable to capture the disorder early enough for effective treatments and therapies. Therefore, exploring new methods such as Alzheimer’s-related changes in brain connectivity might results in earlier and more accurate diagnosis.
What did the authors do and how did they do it?
The authors scanned brains of people with Alzheimer’s Disease as well as healthy individuals by using Magnetic Resonance Imaging (MRI) which is a safe medical test that uses magnets and radio waves to create a detailed picture of brains. They were specifically interested in exploring structural connections between regions that relate to memory. Their next step was estimating functional resting-state networks by using statistical tests on brain areas that displayed simultaneous activity when individuals were laying still in the scanner. The authors then compared the anatomical connections and functional resting-state networks between patients with Alzheimer’s and healthy individuals.
What are the results?
The authors found several differences in brain structural and functional connectivity in patients with Alzheimer’s. The patients’ structural connectivity was reduced between the regions that were linked with problems in memory and attention. The regions specifically linked with memory were also shrunk. In addition to these structural changes, the authors observed reduced activity in functional resting-state networks in Alzheimer’s patients, which is in line with previously published studies.
What do the findings mean going forward for people with the disease?
The authors compared the relevance of measured brain imaging features for clinical practice and concluded that brain connectivity changes related to Alzheimer’s were reflected in many of them. These findings validated that connectivity-related changes in Alzheimer’s disease have the potential to be incorporated in standard screening practices which could improve diagnostic accuracy and result in earlier diagnosis.