Road Skills Hint At "Motion Blindness" Of Alzheimer's
January 31, 2002
Doctors have added to the evidence that patients with Alzheimer's disease lose their way not simply because their memory is failing but because they are subject to a unique form of brain damage that causes symptoms doctors call "motion blindness." Some of the new data comes from driving tests of a small number of patients, where researchers have linked the condition to the loss of one specific driving skill: the ability to stay in one's lane while driving.
"While it's obvious that people with Alzheimer's disease are losing their memory, that's only part of the reason why they become lost," says neurologist Charles Duffy, M.D., Ph.D., who leads the research team at the University of Rochester Medical Center. "These patients also lose their ability to perceive their own motion. That's ultimately what puts them at much greater risk than others of becoming lost."
In the current study, the team studied 26 elderly patients with Alzheimer's disease, 50 healthy elderly adults, and 32 healthy young adults. Scientists performed a variety of tests to measure participants' vision and ability to perceive motion, and then put the Alzheimer's patients who were still driving through a standard New York State driving test.
As in previous studies, older patients had more difficulty with memory than younger patients, and among older patients, Alzheimer's patients had a much harder time detecting motion than their healthy counterparts.
In addition, the 11 Alzheimer's patients who were still able to drive took the driving test: They performed adequately on all aspects of the test except the portion that measures their own knowledge of their location on the road. They tended to drift out of their lane, either across the middle or to the right, and they had difficulty knowing how close or far away they were from the car in front of them.
"These people weren't just bad drivers. They were bad drivers in a particular way," says Duffy. "They couldn't judge where they were in their lane, which mirrors what we've found in the laboratory."
Laura Cushman, Ph.D., a clinical neuropsychologist and associate professor of Physical Medicine and Rehabilitation, arranged the driving tests and analyzed the results. She has studied older drivers for 15 years and is studying ways to predict safe and unsafe drivers. She has found that a combination of three tests that measure concentration, ability to shift attention between tasks, and the ability to see and respond to useful information, pinpoints potentially dangerous drivers very well.
The emotionally charged tussle over when a patient should stop driving takes up hours of Duffy's time with patients and families every week. The American Academy of Neurology advises doctors to tell all patients with the disease not to drive, but Duffy and Cushman would like to see the recommendation modified to take into account an individual's driving ability.
"Losing the right to drive is a tremendous burden; it inflicts further hardship on people who are already having a very difficult time," says Duffy. "If we can understand who is really at risk for having difficulty driving, and for getting lost--if the disease didn't mean the kind of loss of independence it now means for most people--that would be significant. It's crucial not to be arbitrary."
Cushman agrees, and she recommends that concerned family members have the patient tested by a driver rehabilitation and assessment service such as Rochester Rehabilitation Center, which tested the patients in this study.
"Most doctors agree that in the early stages of the disease, patients can still drive safely, but the family needs to be aware that the disease is progressive, and that at some point, the person will no longer be able to drive, and he or she will need assistance to realize this," says Cushman. "The only way to assess an individual's driving ability is to do a real-life test on the road."
Because of the small number of drivers tested in the current study, which was published in Cerebral Cortex, Cushman says the specific drift-from-lane result should be considered preliminary. Driving skills of both people with Alzheimer's and healthy people should be studied more closely, she says, before the ability to stay in one's lane becomes part of any test measuring Alzheimer's disease.
The doctors and scientists are using the work to launch an array of studies. One goal is a laboratory test that could pinpoint those patients who will have a problem driving, which would allow other patients to continue driving with confidence.
Also on the team's wish list is a device to help patients perceive their motion more fully while driving. Alzheimer's patients usually need at least twice as much visual stimulation than healthy people to understand their motion, Duffy says. A display or "cognitive prosthesis" that draws out and maximizes such information in an easy-to-see manner could help drivers stay on the road longer, Duffy believes.
Currently Duffy and Cushman are creating a virtual-reality program to assess and possibly improve a patient's ability to get around. The virtual world could be a place where patients practice their navigation skills, perhaps practicing to drive around their neighborhood or walk around their house or a local mall. "How much can experience in a virtual environment help navigate a real environment?" asks Duffy. "It may be that virtual experience is as good as real experience, or even better, because you could highlight features in the environment that would train people to look for certain things."
Duffy first reported the phenomenon of motion blindness three years ago, when he found that many Alzheimer's patients have much greater-than-normal difficulty detecting motion as they move in the world. While it's tempting to think that patients get lost or become disoriented simply because they forget information such as where they live, Duffy found that memory failure explains only a small part of why patients become lost. Instead he found that brain damage in a highly specialized part of the brain that interprets motion leaves the patients unable to perceive motion in a way that most people unconsciously do all the time.
"Relying on your memory to get around is a strategy of the young and healthy," says Duffy. "In people with Alzheimer's, once they begin losing their memory, the nervous system adapts and patients instead rely on their perception of self-movement. But once their ability to detect motion goes, they've lost all the tools in their tool chest for finding their way around.
"Imagine having that pit-in-the-stomach feeling of getting lost all the time. For these patients, it's always like they're in a brand new place. You are just plain lost, nearly all the time; you might as well be nowhere. It's a very sad state of affairs, and it has a tremendous impact on quality of someone's life."
A prickly patient was the first to make Duffy think that more than memory is involved with the disorientation of Alzheimer's patients. Duffy visited a patient who said he had trouble getting where he wanted to go. "I assumed he just forgot where he was going or how to get there, but the patient was indignant. The patient said he simply lost track of where he was, not that he forgot where he was going." For years Duffy had studied motion perception, and he recognized that the man's description sounded like what would happen if there were damage to the brain region that governs self-movement. The encounter steered Duffy toward a new career path studying Alzheimer's disease.
Duffy and Cushman's colleagues on the project, which was funded by the National Institute on Aging and the Alzheimer's Association, include medical student Hope O'Brien, former technician Sheldon Tetewsky, former faculty member Lisa Avery, and faculty member Walter Makous.