Conventionally defined MCI has reasonable predictive value and specificity for AD. However, MCI was very unstable across time in this study. Furthermore, the definition of MCI seems to be too restrictive and should probably be extended to other categories of individuals also at high risk of developing AD.

Better knowledge of the preclinical phase of Alzheimer's disease would be an important advance to allow earlier treatment of this ominous disease. This prodromal period was investigated in the Paquid cohort by analysing change in cognitive performances at five time points over a 9 year period. Neuropsychological measures including global cognitive functioning (Mini-Mental State Examination), visuo-spatial memory (Benton Visual Retention Test), verbal fluency (Isaacs Set Test) and abstract thinking (Wechsler Similarities Test) were assessed in 215 future Alzheimer's disease subjects and 1050 individuals without dementia. The results showed that cognitive performances of the pre-morbid subjects at baseline were already lower than those of individuals without dementia (1.4 points less on the Mini-Mental State Examination; 1.8 points less on the Benton Visual Retention Test; 4 points less on the Isaacs Set Test and 0.8 points less on the Wechsler Similarities Test). For some neuropsychological tests, an acceleration of the decline occurred approximately 3 years before the diagnosis and, for each test, the course of decline was modulated by education level. These findings show that abnormally low performances can be evidenced 9 years before the clinical diagnosis of Alzheimer's disease in several domains of cognition beyond memory and that cognitive change over time can be influenced by education.

Some studies have suggested that people with a high educational level have a lower risk of developing dementia compared to people with a low educational level. This protective effect of education has been explained by the constitution of a cognitive reserve which might delay the cognitive and functional expression of neurodegenerative illnesses. The aim of this study is, on the one hand, to evaluate the impact of education on cognitive functioning, which is thought to support the cognitive reserve capacity, and on the other, to determine the extent to which cognitive functioning is affected by other explanatory variables. The analysis was conducted on 1022 individuals without physical or neurological disorders in the Personnes Ages Quid study. These participants were aged 66 and over and had completed a neuropsychological battery. The effect of some demographic and socioeconomic variables on cognitive performance was also analyzed. Multivariate analysis showed a significant effect of education on most neuropsychological performances, independently of the other variables, and more particularly, in the high-attention-demanding tests. A principal component analysis demonstrated that education specifically increases 2 cognitive components: controlled processes and conceptualization ability. More-over, mental stimulation occurring after the education years, such as high-complex-activity occupations, seems to increase the controlled component. All these results suggest that the effect of education on cognitive reserve may be explained by an in-crease in controlled processes and conceptualization abilities. These 2 cognitive components might delay the clinical expression of neurodegenerative illnesses by maintaining global cognitive efficiency. Of these 2 components, controlled processes were also influenced by high attention-demanding occupations.

Several recent studies have provided substantial support for the proposal that a decrease in inhibitory processing may play an important role in cognitive changes occurring in the early stages of Dementia of the Alzheimer Type (DAT). The question addressed by the present study was whether these deficits are the result of the failure of a general inhibitory mechanism, or whether DAT is associated with selective decreases in a subset of inhibitory processes. For this, a computerized battery of tasks assessing several inhibitory mechanisms was administered to 28 mild DAT patients and 28 matched elderly adults. The results showed that DAT patients failed to produce Negative Priming effects and were severely impaired in the Stroop task. However, no evidence was found for an impairment on the Go-No go task and only limited impairment on the Stop Signal task, suggesting that in the early stages of the disease, not all inhibitory mechanisms are uniformly impaired.

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