In a new study, researchers have discovered an early disruption in the process of memory formation in older humans who exhibit some early brain changes associated with Alzheimer's disease (AD) but show little or no memory impairment.
The study sheds light on the role of amyloid protein in memory impairment and may lead to development of strategies for predicting and treating cognitive decline in individuals who are at-risk for AD.
AD is primarily characterised by the accumulation and deposition of neuron-damaging clumps of amyloid protein.
In earlier studies, researchers have suggested that amyloid deposition begins many years prior to the onset of clinical symptoms.
However, the exact link between amyloid deposition and memory impairment has not been clearly demonstrated in humans.
"Two recent advances in neuroimaging now allow us to explore the early, asymptomatic phase of AD, the ability to measure amyloid distribution in living humans and the identification of sensitive markers of brain dysfunction in AD," explained lead study author, Dr. Reisa Sperling from the Center for Alzheimer's Research and Treatment at Brigham and Women's Hospital in Boston.
Apart from amyloid accumulation, AD has been associated with functional alterations in a specific network of brain regions that are intimately linked with memory formation.
The researchers combined amyloid imaging with an associative memory functional brain-imaging paradigm to study older humans who did not exhibit significant memory impairment.
Particularly, the researchers found that a significant number of nondemented older individuals exhibited amyloid deposition and abnormal neural activity in key areas of the brain network thought to be involved in successful memory function.
The results have for the first time demonstrated that amyloid pathology in asymptomatic older humans is linked with aberrant neural responses during the process of memory formation.
"Longitudinal studies are certainly needed, but our findings are consistent with the premise that cognitively intact older individuals with amyloid pathology may already be in the early stages of AD.
The combination of molecular and functional imaging techniques may prove useful in monitoring disease progression prior to significant clinical symptoms, as well as the response to amyloid-modifying therapeutic agents in subjects at-risk for developing AD," explained Sperling.
The study has been published in the latest issue of the journal Neuron.