[Automatic recall of didactic knowledge in semantic memory during normal aging and in Alzheimer's disease]

The goal of our work is to study the most consolidated items of semantic memory in normal subjects and in patients with Alzheimer's disease (AD).

The first test is based on automatic recall of didactic knowledge. This test is made of 250 automatic verbal expressions exploring general knowledge. It as been validated according to age and cultural levels in 219 normal subjects (20-90 years old). Another simplified test called EVA including only 50 of the 250 previously chosen items was also used. The EVA scores found in a normal population have been classified by centilages according to age and cultural levels. The EVA was also tested in 20 patients with AD and the results compared with MMSE and "Pyramids and Palm Trees Test" (semantic memory testing).

The results reveal that the scores observed with the first test in a normal population with comparable cultural levels are correlated with age. EVA test scores found in control subjects show that the median value, for a same age group, is positively correlated with cultural levels. In patients with AD, scores for EVA test and MMSE are associated, the low results being linked to the severity of dementia. In addition, scores for EVA test and "Pyramids and Palm Trees Test" are also significantly correlated. Seven patients with mild dementia (MMSE>20) have abnormal scores for the "Pyramids and Palm Trees Test".

Our study confirms that changes linked to aging do not involve all aspects of cognition. The most consolidated items of semantic memory assessed by EVA test seem to resist at the beginning of AD but later decline similarly to the other items of semantic memory. Normal results for EVA tests do not imply that semantic memory is not affected in the early phases of AD. We propose this new test which assesses the semantic memory stock without involving an active process of recuperation. This test is not suitable for an early diagnosis of AD but could help to evaluate the severity of the disease during the evolution.