The findings could improve early detection of the disease, when drugs may be most effective. The study was published in the online edition of the journal Nature Neuroscience, reports Science Daily.
"It has been known for years that Alzheimer's starts in a brain region known as the entorhinal cortex," said senior co-author Scott A. Small, director of the Alzheimer's Disease Research Center.
"But this study is the first to show in living patients that it begins specifically in the lateral entorhinal cortex, or LEC," he said.
"The LEC is considered to be a gateway to the hippocampus, which plays a key role in the consolidation of long-term memory, among other functions. If the LEC is affected, other aspects of the hippocampus will also be affected," Small added.
The study also shows that, over the time, Alzheimer's spreads from the LEC directly to other areas of the cerebral cortex, in particular the parietal cortex, a brain region involved in various functions, including spatial orientation and navigation.