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Why Alzheimer's patients could forget that zebras have stripes

December 21, 2010 - Washington

A normal person wouldn't forget that a zebra has stripes or that a giraffe has four legs because these are concepts related to semantic memory - something that allows us to assign meaning to words and to recall general knowledge that we have learned.

Now, a group of scientists has identified the elements of semantic memory, which are the first to deteriorate, and may have thus provide important insights into how Alzheimer's disease develops in the early stages.

Mickael Laisney and colleagues, from the university hospitals of Caen and Rennes, studied the word-recognition abilities of 16 Alzheimer's patients and 8 patients with semantic Dementia.

Due to an effect known as semantic priming, people tend to more quickly recognise a word (e.g., "tiger") if they have previously seen a related word (e.g.,"lion").

The study has shown that that the first elements of semantic memory to deteriorate are the distinguishing characteristics of a concept, such as a zebra's stripes or a giraffe's long neck.

From here on, concepts get blurry, like, zebras and giraffes becoming generic four-legged African mammals.

Authors conclude that this is the reason why patients temporarily find it easier to recognise related words in the early stages of Memory loss. The effect disappears in later stages of the disease.

Their findings are published in the January 2011 issue of Cortex.


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