New cause for Alzheimer's symptom found

Study says that 'motion blindness' affects disorientation

A previously unobserved condition in some Alzheimer's patients that physicians are calling "motion blindness" is a big reason such patients become disoriented and lose their way, asserts a University study in the March 23 issue of Neurology.

Duffy

For years doctors generally have thought that Alzheimer's patients become lost simply because they forget directions or where they're going. But the Rochester team has found that while Alzheimer's patients certainly do have memory problems, those are separate from the motion blindness that is due to brain damage in a highly sophisticated part of the brain that interprets motion.

"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," said lead author Charles Duffy, a neurologist at Strong Memorial Hospital. "Many of these patients are basically blind to the kinds of cues most of us absorb unconsciously every day. It's a disorder of perception as well as memory," added Duffy, associate professor of neurology and ophthalmology, and a member of the Center for Visual Science.

The findings are based on experiments in Duffy's Visual Orientation Laboratory. Patients sit in a chair and watch computer-generated moving patterns of dots of light on a screen eight feet high and six feet wide. The moving dots form patterns--like snowflakes rushing at the windshield as someone drives through a storm --that people's brains use to understand how they're moving. In a car the way the flakes part helps most individuals realize they're moving forward. Alzheimer's patients would see the flakes move, but they would have a much harder time understanding what this tells them about their own movement. The study found that Alzheimer's patients needed nearly twice as much visual information--more dots traveling in the same direction--to understand the patterns.

These results create the possibility of pinpointing which Alzheimer's patients will encounter serious difficulty driving or getting around their neighborhoods, or even their own homes. That would allow some patients to live independently longer than they otherwise might, while alerting other families that they should be extra vigilant in keeping tabs on their relatives. It should also spur health care providers to encourage patients to refer to specific landmarks that are independent of motion when getting around.

Assisting Duffy in the study were researchers Sheldon Tetewsky and Hope O'Brien and physician Lisa Lebedovych.