Alzheimer's Muddles Memory of How Things Work

CREDIT: © Laurin Rinder | Dreamstime.com View full size image

Which is bigger, a key or an ant? That question might be easy for you to answer quickly, but it could be a little more confusing for a person with Alzheimer's.

The most obvious trait of the mind-ruining disease is memory loss, with patients forgetting once-familiar people, places and experiences. New research shows how this mental deterioration extends to semantic memory, which has more to do with remembering facts and concepts and underlies a basic understanding of how things works.

For their study, researchers recruited 70 cognitively healthy people, 27 patients with Alzheimer's 25 patients with mild cognitive impairment (MCI), often considered a precursor to dementia. All were tested on their ability to make size judgments about two pictures shown to them — the premise being that the bigger the difference in size between two objects, the faster a person would be able to answer the question.

"If you ask someone what is bigger, a key or an ant, they would be slower in their response than if you asked them what is bigger, a key or a house," researcher Terry Goldberg, of the Hofstra North Shore-LIJ School of Medicine, said in a statement.

This held true in the experiments, but the MCI and Alzheimer's patients had much more trouble when asked to respond to a task with small size differences.

The experiment was then tweaked so that the participants were shown pictures of a small ant and a big house or a big ant and a small house. The MCI and Alzheimer's patients did not have a problem making judgments about the small ant and big house, but had trouble with the more incongruent set. They were confused about which object was actually larger when shown a big ant and a small house, and were more likely to answer incorrectly or take longer to arrive at a response, the researchers said.

Goldberg said the findings indicate "that something is slowing down the patient and it is not episodic memory but semantic memory."

The team will continue to study these patients over time to see if these semantic problems get worse as the disease advances.

The research was detailed this month in the American Journal of Psychiatry.

Follow LiveScience on Twitter @livescience. We're also on Facebook & Google+.