A new discovery shows a tiny section of the brain responsible for orienting ourselves with the surrounding environment is susceptible to damage from Alzheimer’s disease. This finding helps explain why people with Alzheimer’s can become easily lost. This is according to a University of Rochester Medical Center report appearing in the March 29 issue of the journal Science.

Neurologist Charles Duffy, M.D., Ph.D. had previously discovered a small section of brain tissue slightly above and behind the ear known as the medial superior temporal area (MST). The MST acts much like a compass, instantly updating your mental image of your body's movements. In a new study, Duffy and graduate student Michael Froehler found that the MST acts not only as a compass but also as a sort of biological positioning system, providing a mental map to help us understand exactly where we are in the world and how we got there.

Previous research has shown that brain cells in the MST die in great numbers in patients with Alzheimer’s disease, and four years ago Duffy described a condition known as "motion blindness" that explained why Alzheimer's patients lost the ability to keep track of their own movements; however, his new research has found that the same region is even more crucial than previously thought for keeping us oriented.

"We believe this discovery will help us develop new ways to treat people with Alzheimer's disease who lose the ability to understand where they are or where they're going," says Duffy. "For these patients it's truly a tragedy when the disease reaches a point where they can't find their way through their town, their neighborhood, or even their own home; often this is the first step toward a huge loss of independence. Understanding the damage done by Alzheimer's disease is our best hope toward finding our way to treatments and prevention."

There are many reports of patients who scramble to find routines and make their way around despite the void left by the ongoing death of their brain cells.

"One former patient would drive from her home to visit her husband in a nursing home every day. She'd get in the car, drive a couple of miles, then lose track of where she was - so she'd pull over, get out and walk around looking for a building or some other landmark to remind her of where she was. Then she'd get back in the car, drive a couple more miles, lose track of where she was, and do the same thing, over and over again, until she reached her destination. She did this day after day."

This patient had lost her ability for dead reckoning, or what scientists call path integration - the ability to figure out where you are based on the knowledge of where you started and how you moved. If your house is two blocks west of a grocery store and you leave your house and walk two blocks west, it's the sense of dead reckoning that tells you to expect a grocery store when you arrive.

It's this ability that Froehler and Duffy discovered resides in the MST. Scientists have known for more than a decade that the MST governs the ability to understand self-movement - where you're headed at that very moment. The team showed that the same brain region provides some overall context to help identify one’s location. In the example above, the MST not only tells you you're heading west at the moment, but it provides the context and knowledge for you to realize that a grocery store should appear two blocks away.

"There's a continuous interaction between where you've been, where you're going, and where you are. What we've done is peeked into that process," says Duffy. "Path integration or dead reckoning is crucial to our ability to navigate the world. It's the difference between turning right and heading down the road, or turning right and ending up in a ditch. In both cases you're turning right, but the significance of your moment-by-moment heading depends on the context in which it occurs."