Sept. 26 (HealthDay News) -- A specific pattern of brain activity could be a sign of early Alzheimer's disease, U.S. researchers report.

They noted that as new treatments for Alzheimer's become available, spotting the disease early will become critical.

A team at Duke University Medical Center in Durham, N.C., used functional magnetic resonance imaging (fMRI) to study the brains of 13 patients with mild Alzheimer's disease, 34 patients with mild cognitive impairment, and 28 healthy people (averaging about 73 years of age) as they did a memory task.

Participants with mild Alzheimer's and mild cognitive impairment showed impaired activity in the medial temporal lobe (MTL), an area of the brain associated with episodic memory that normally turns on during a memory task. Previous research had found that structural changes in the MTL are among the earliest known brain changes in people with Alzheimer's disease.

More surprisingly, the researchers found impaired deactivation in the posteromedial cortex (PMC), a brain area involved in personal memory that's usually suppressed during a memory task. The degree of PMC deactivation was closely related to the level of a patient's memory impairment and significantly correlated with their neuropsychological testing scores.

"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," study lead author Dr. Jeffrey R. Petrella, an associate professor of radiology at Duke, said in a prepared statement.

He said the findings "implicate a potential functional, rather than structural, brain maker -- separate from atrophy -- that may help enhance diagnosis and treatment monitoring of Alzheimer's patients."

The study is published in the October issue of the journal Radiology.

SOURCE: Radiological Society of North America, news release, Sept. 25, 2007