Alzheimer's Brain Can't Block Distractions

Sept. 21, 2005 -- The brain of a person with Alzheimer's disease may have lost the ability to block out irrelevant information and focus on the task at hand, according to a new study.

Like closing your eyes when listening to music or wearing earplugs when you read, researchers say a healthy brain follows a similar strategy and automatically blocks distracting sensory stimulation to increase concentration.

But their findings show this focusing process may be defective in people with Alzheimer's disease and contribute to their disability.

Alzheimer's Disease Affects Concentration

Previous studies have shown that when healthy people perform tasks that depend on one type of information, such as listening to music, they only activate the areas of the brain involved in auditory processing and deactivate the areas that deal exclusively with visual clues in order to increase concentration.

To determine whether this process is affected by Alzheimer's disease, researchers compared activation/deactivation patterns in the brains of 10 people with moderate Alzheimer's disease, 11 healthy people, and 11 people with mild cognitive impairment.

The participants were trained to perform a virtual reality navigation task that relied on purely visual cues, and underwent brain imaging scans immediately after completing the task.

The results showed that healthy people deactivated the area of the brain that deals with auditory clues to complete the task, while this auditory deactivation was much less prominent in people with mild cognitive impairment and completely absent in people with Alzheimer's disease.

Researchers say the findings show that Alzheimer's patients' disorientation with their surroundings may be partially caused by their inability to focus brain activity on the relevant task.