Writing about their findings in the journal Radiology, the researchers revealed that they used functional magnetic resonance imaging (fMRI) technique in their study.
"The findings of this study implicate a potential functional, rather than structural, brain marker—separate from atrophy—that may help enhance diagnosis and treatment monitoring of Alzheimer's patients," said the study's lead author, Dr. Jeffrey R. Petrella, associate professor of radiology at Duke University Medical Center in Durham.
Since there is no cure for Alzheimer's disease, early diagnosis of the condition is crucial in order that the patients could be administered proper treatment.
"As new therapies for Alzheimer's disease enter the pipeline over the next five years, early diagnosis will become critical for patient selection. fMRI may play a key role in early diagnosis, when combined with clinical, genetic and other imaging markers," Dr. Petrella said.
Thirteen patients with mild Alzheimer's disease, 34 patients with mild cognitive impairment, and 28 healthy controls comprised in the study group, which included 37 men and 38 women with a mean age of 72.9 years. After completing standard neuropsychological testing, the study participants were monitored with fMRI while performing a face-name associative memory task.
The researchers observed increasingly impaired activation in the MTL—an area of the brain associated with episodic memory that normally turns on during a memory task—along the spectrum from healthy people at low risk, to people with mild memory problems, to patients with Alzheimer's disease.
They also saw increasingly impaired deactivation in the posteromedial cortices (PMC), an area recently implicated with personal memory that normally suppresses its activity during a memory task.
According to the researchers, the magnitude of deactivation in the PMC was closely related to the level of memory impairment in the patients, and significantly correlated with their neuropsychological testing scores.
Several previous studies had suggested that MTL activation might be a possible marker of Alzheimer's. However, Dr. Petrella said that deactivation in the PMC might represent a more sensitive marker of early diagnosis of the disease.
"In other words, the brain not only loses its ability to turn on in certain regions, but also loses its ability to turn off in other regions, and the latter may be a more sensitive marker. These findings give us insight into how the brain's memory networks break down, remodel and finally fail as memory impairment ensues," Dr. Petrella said.
The researchers have revealed that they are now planning to conduct a multicenter study to determine whether fMRI can be combined with other imaging and genetic tests to scan for future disease.
"Much like a negative colonoscopy gives you reassurance, a normal fMRI may, in the future, also offer predictive value," said study co-author Dr. P. Murali Doraiswamy, chief of the Division of Biological Psychiatry and Alzheimer's clinical trial expert at Duke.