High-resolution magnetic resonance (MR) imaging studies have identified characteristic changes in brain structure — thinning of key cortical regions and reduced volume of structures such as the hippocampus — in persons with mild cognitive impairment, in individuals known to carry gene mutations that directly cause Alzheimer’s disease, and in diagnosed Alzheimer’s patients.
The current study, published in the Annals of Neurology, involved 87 cognitively normal older individuals and 32 patients diagnosed with mild Alzheimer’s (matched for age, gender and education) who had enrolled in the long-term Harvard Aging Brain Study. Participants underwent both high-resolution MR imaging of brain structure and PET scanning with PiB to detect amyloid plaques.
The results showed that those cognitively normal individuals who had amyloid plaques also had structural changes similar to but less pronounced than the neurodegenerative changes seen in the symptomatic patients. Structural changes were most evident in areas comprising what is called the default network, which is known to be affected early in the course of Alzheimer’s disease.
The study was well conducted, well controlled and used the latest techniques in brain imaging. This paper provides further evidence that amyloid deposition is occurring in the brain decades before the dementia stage begins, and in fact, even before cognitive impairment develops. It also supports the idea that the mechanism by which cognitive impairment and dementia arise is due to atrophy, or shrinkage, of the brain in selected areas as a consequence of beta-amyloid deposition.