Cognitive robustness in Alzheimer\'s Disease Patients

Empirical semantic networks constructed from word association data represent a good map for conceptual knowledge storage and retrieval. Concepts, represented as words, link each other with a certain weight representing the strength of their relation. Everyday experience shows that, in general, word search and retrieval processes, which can be assimilated to traversals of the semantic network, emerge providing fluent and coherent speech, i.e. are efficient and robust. However, the are some diseases, in particular Alzheimer's Disease (AD), which irremediably alter the efficiency of such processes. One of the most striking alterations is the effect of hyperpriming in AD patients. Here we show that the hyperpriming alteration can be totally understood in the scope of a progressive degradation of the semantic network topology. Our study shows that hyperpriming is the result of the disconnection of the weakest links in the semantic network, which in turn relatively reinforces the remaining existing connections. We compare our simulation results with previous empirical observations in real patients finding a qualitative agreement. The network approach presented here can be used as a complementary tool to accomodate actual theories about impaired cognition.

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