[Semantic memory in Alzheimer's disease: contributions of semantic priming]

Patients with Alzheimer's disease can be affected by semantic memory disorders from the onset of the dementia. Knowing precisely these disorders is important to improve the early diagnosis of Alzheimer's disease. Classical tests of semantic memory, such as naming and verbal fluency, highlight the existence of semantic disorders in the first stages of the disease. However, these tasks are not specific and involve cognitive processes (working memory, attentional resources), which are often disturbed in Alzheimer's disease. Therefore, they cannot attest the origin of the semantic disorders, which can be related either to a deficit of access to stored information in a preserved semantic network, or to the deterioration of the semantic memory network. Semantic priming paradigms, by minimizing the intervention of processes other than semantic, constitute relevant tools to study the integrity of the semantic network. However, the results of the studies devoted to the semantic priming effects in patients suffering from Alzheimer's disease are heterogeneous. This could be imputed, in part, to differences in experimental procedures. Nevertheless, some studies, conducted with a very controlled methodology, showed that semantic relationships used in the semantic paradigm as well as the semantic deficit severity have a serious impact on semantic priming effects. Taking into account these parameters, the results of semantic priming studies are more in accordance with the assumption of a storage degradation than with an access deficit. Moreover, these studies, and especially the observation of an hyperpriming effect, allow a better understanding of how semantic memory is degraded. The progressive deterioration begins at the level of the concept attributes, and further involves the concepts themselves.