The brains of people with mild cognitive impairment, a stage before the onset of Alzheimer's, do not exhibit the same physical changes, leading researchers to identify two different neurological pathways to the disease, a new study has found. 

The research, conducted by scientists at UCLA and the University of Pittsburgh School of Medicine, appears in the Archives of Neurology. 

Using a new neuro-imaging procedure which creates three-dimensional maps of the brain, researchers were able to detect different levels of tissue degeneration in the hippocampus, the part of the brain critical to memory. 

The tests were performed in persons with MCI, a transitional stage between normal cognition and Alzheimer's. MCI is broken down into two sub-types -- one marked by isolated memory impairment and the other by mild or no memory loss, but with problems in judgment or language. 

The study found that persons with the type involving only memory loss had significant shrinkage of the hippocampus, as great as that of patients who already had Alzheimer's disease. These patients also were part of the study. Meanwhile, the hippocampus in persons with no memory loss, but other types of impairment, was almost normal. 

Interestingly, both pathways of MCI eventually led to Alzheimer's disease. 

"What this tells us is that there is not a single way that people get to the disease," said lead study author James T. Becker, a neuropsychologist at the University of Pittsburgh School of Medicine. "Now we can investigate these pathways and develop treatments that, we hope, may slow or stop the progression of Alzheimer's." 

The study is the first to use such modeling technology to visualize changes in the brains of people with MCI, which Becker identified as a relatively new area of Alzheimer's research. Until now, he said, it was not known if the pathologies of the two types of MCI were different. 

Alzheimer's affects nearly 5 million Americans, the majority of whom are age 65 or older. 

In the study, 3-D MRI imaging data was taken on six patients with memory loss only, 20 patients with no memory loss but other types of impairment, and 20 people with Alzheimer's disease. The creation of 3-D mesh reconstructions of each patient's hippocampus allowed researchers to see where the structure had deteriorated. 

"What this gives us is a way of looking at where the damage occurred in the structure, which now means a better way of tracking disease and the response to medication," Becker said. 

Maria Carrillo, director of medical and scientific affairs for the Alzheimer's Association, called this new type of imaging a "potentially great tool in the Alzheimer's research arena."