Dec 20, 2010 14:13 GMT  ·  By
According to one geneticist, one out of every 2.5-3 million zebras are blonde.
   According to one geneticist, one out of every 2.5-3 million zebras are blonde.

A group of French neurologists and neuropsychologists have identified which elements of the semantic memory are the first to be affected by dementia and discovered an explanation to hyperpriming – a phenomenon that appears in the early stages of Alzheimer's disease.

Semantic memory is the ability to remember things like the fact that the zebra has stripes and that a giraffe is a four-legged animal.

It's what allows us to associate words with meaning, and to remember general knowledge and concepts we have learned.

When this ability deteriorates, it is a sign of semantic dementia that can also happen in Alzheimer’s disease, AlphaGalileo reports.

The research was carried out by Dr Mickaël Laisney and colleagues, from the university hospitals of Caen and Rennes, and they focused on the word-recognition abilities of 16 Alzheimer’s patients and 8 patients with semantic dementia.

The patients saw pairs of words in succession and were asked to say whether they recognized the second word in each pair.

Through this, the researchers wanted to see how the semantic priming effect worked in these patients, whether they recognized faster a word if it was preceded by a related word (tiger – lion).

A previous study concluded that the semantic priming effect increased in the early stages of Alzheimer's disease, so the patients recognized related words much faster than healthy participants.

In a way it is quite strange since the hyperpriming phenomenon is the opposite of the idea of memory loss in Alzheimer's patients.

Still, this last study has clarified the situation a bit, by finding out that the first element of semantic memory to fail, is making the difference between the characteristics of a concept – a zebra's stripes and a giraffe's long neck.

This causes a confusion, and the zebra and the giraffe become just four-legged African animals.

The researchers say that this is why patients find it easier to recognize related words, during the early stages of memory loss, but this effect disappears in later stages of the disease.

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