The Rochester Review, University of Rochester, Rochester, New York, USA
By Tom Rickey
"People with Alzheimer's get lost not because they can't remember where they've been, but because they can't see where they're going," says Charles Duffy, a Rochester neurologist and lead investigator in a study published last spring in the journal Neurology.
A previously unobserved condition in some Alzheimer's patients, which physicians are calling "motion blindness," is a big reason such patients become disoriented, Duffy reports.
For years, doctors generally have thought that Alzheimer's patients get lost simply because they forget directions or can't remember where they were going. But the Rochester team has found that while these patients certainly do have memory problems, the memory loss is separate from the problem caused by damage in a highly sophisticated part of the brain that interprets motion.
"Many of these patients are basically blind to the kinds of cues most of us absorb unconsciously every day," Duffy says. "It's almost like they're walking around with their eyes closed. Alzheimer's is a disorder of perception as well as of memory."
Some 4 million Americans have this cruel disease characterized by a gradual loss of cognitive abilities accompanied by behavioral symptoms such as agitation, aggression, and depression, along with the already-noted memory loss and tendency to wander.
It's named for the German neurologist Alois Alzheimer (1864-1915). In 1906, he chanced to autopsy the brain of a 56-year-old woman who had suffered progressive mental deterioration for several years before her death. Using the then new technique of tissue staining, he discovered the mysterious tangles of nerve cells that distinguish the disease and speculated that they might have been the cause of her dementia. When later autopsies turned up the same abnormalities in the brains of similarly afflicted individuals, an eminent German psychiatrist suggested that the illness be called after his colleague.
Nearly a century later, many of the mysteries of the disease are still unexplained, and a cure is not yet in sight. But recent discoveries have led to promising treatments, and some researchers are even (cautiously) predicting that within the next decade or so Alzheimer's might become a reasonably manageable chronic illness, rather like diabetes or asthma.
Meanwhile, scientists like Duffy are attempting to unlock the remaining secrets of the disorder in laboratories around the world.
An associate professor of neurology and ophthalmology and a member of the Center for Visual Science, Duffy does his work in a lab tucked into the third floor of the University's Medical Center. It was here that he and his colleagues made their finding about motion blindness, thanks to a Star Trek-like device consisting of a computer and a big TV-projection screen on which an endless series of points of light races toward the viewer.
The moving dots form patterns on the screen much like snowflakes rushing at the windshield when you're driving through a storm. The way the snow parts in front of you lets you know that you're going forward. But although many Alzheimer's patients can see that the flakes are moving, they have a much harder time taking in what this tells them about their own movement.
(It's the ability to correctly interpret motion that helps you understand, for instance, you're the one going 60 miles an hour down a country road, not the cows and barns that appear to be whizzing past.)
The new research creates the possibility of pinpointing which patients will encounter serious difficulty while driving or trying to get around their neighborhoods, or even around their own homes. Identifying the patients subject to motion blindness would alert their families to the need for extra vigilance in keeping tabs on them. It should also spur care providers to encourage these patients to refer to stationary landmarks as aids to successful navigation.
Like most neurologists, Duffy sees Alzheimer's patients who regularly complain about getting lost. "I hear the same story over and over from new patients and their families. The world becomes a strange place, and the street they've lived on for 30 years becomes unfamiliar."
Duffy, who holds both an M.D. and a Ph.D., was part of the research team that several years ago first identified the part of the cerebral cortex that interprets self-movement, and he recognized that the symptoms his patients complained about could result from damage to this brain area.
So, with funding from the National Institute on Aging and the National Eye Institute, Duffy decided to test patients' abilities to interpret the "optic flow field," the scientific term for the motion you see as a result of your own movement.
Together with researchers Sheldon Tetewsky and Hope O'Brien and physician Lisa Lebedovych, Duffy tested 6 healthy young adults, 12 healthy elderly adults, and 11 elderly Alzheimer's patients by having them sit in front of the pattern of moving dots and press buttons to indicate in which direction the dots seemed to be going.
The scientists found that while the ability to interpret motion diminished slightly with increasing age, people with Alzheimer's were much more likely to suffer from motion blindness, needing nearly twice as much visual information--more dots traveling in the same direction--to understand the patterns.
In another part of the experiment, research subjects were escorted between the front lobby of the University's Medical Center and the Visual Orientation Laboratory, then were asked questions about the route. The results: On average, the young ones answered 88 percent of the questions correctly, the healthy elderly answered 73 percent correctly, and the Alzheimer's people got only 32 percent right.
The ability to perceive motion was not, however, diminished in all the Alzheimer's patients in the study. Of the 11, only 6 did poorly analyzing the optic flow field; they were also the ones who had the most difficult time remembering the way to the lab. Duffy thinks the research may form the basis for a test that would allow doctors to monitor patients closely, perhaps even predict more accurately the impact of the disease on a patient's ability to live alone or to drive.
"If these people can't find their way, the car keys are taken away and they're basically locked in their house. This loss of independence can be devastating," Duffy says. "Right now doctors don't have a way of assessing who should be told to stop driving and who might be safe to continue regardless of age. Now we've identified one ability that may help pinpoint that."
Because the veil of confusion that comes with Alzheimer's is so evident, most people think that it's mainly the hippocampus--our memory center--that is ravaged by the disease. But pathologists know that the disorder also wipes out neurons in an adjacent part of the cortex where the temporal, occipital, and parietal lobes come together. It's this highly sophisticated processing hub that is home to our ability to interpret motion.
While both areas are ultimately damaged, in the early stages the illness usually seems to affect one area more than the other.
"Some patients will lose their way, and others will lose their memory," says Duffy. There are patients who continue to drive years after diagnosis though they can't remember their son's name or whether or not they have a job. Others can't even walk out their front door without getting lost, even though they have a firm grip on the circumstances of their lives.
Regardless of the way the disease manifests itself, the symptoms of Alzheimer's should not be accepted as an inevitable result of getting older, Duffy says.
"We shouldn't allow our elderly relatives to dwindle away under the misimpression that such declines are part of normal aging and there's nothing we can do about it. There is something we can do about it--and it is cruel to deprive these people of appropriate treatment."
Tom Rickey is senior science editor for the Office of University Public Relations.
Copyright 1999, University of Rochester