Why Would Alzheimer’s Patients Perform Better on a Memory Test?

A recent study by Mickael Laisney and his colleagues that was summarized in the APS Observer1 replicated certain paradoxical results and provided an interesting explanation for the paradox. They studied the word-recognition abilities of 16 Alzheimer’s patients and eight patients with semantic dementia. Their performance was compared against healthy patients not suffering from these disorders. The patients were shown pairs of words in succession and were asked to indicate whether they recognized the second word in each pair. There is an effect known as semantic priming whereby a word is recognized more quickly (“zebra” for example) if they had recently seen a related word (“giraffe”). Patients in the early stages of Alzheimer’s disease exhibit a paradoxical “hyperpriming” effect whereby they show a more pronounced priming effect than do normal control subjects. So why should people suffering from a memory disease perform better on a memory test than people not suffering from this disease?

Laisney and his colleagues offered an explanation regarding why these patients perform better. They showed that the first elements of semantic memory to deteriorate were the distinguishing characteristics of a concept such as the stripes of a zebra or the long neck of a giraffe. Once these distinguishing characteristics are lost, zebras and giraffes become generic four-legged mammals. So the concepts become more related and the priming effect increases during the early stages of the disease. As the disease advances, this hyperpriming effect disappears.

This is an interesting effect and explanation that does provide some insight into the progress of the loss of memory in Alzheimer’s and semantic dementia. However, it should be understood that this is not a test for Alzheimer’s disease. Alzheimer’s should be diagnosed by a professional, both to increase the accuracy of the diagnosis and to begin a regimen for treating the disease.

1“When the Zebra Loses Its Stripes” APS Observer February 2011, 7.

© Douglas Griffith and healthymemory.wordpress.com, 2011. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Douglas Griffith and healthymemory.wordpress.com with appropriate and specific direction to the original content.

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