Cognitive process in preclinical phase of dementia

Abstract

Several recent prospective studies have demonstrated the existence of a preclinical stage of dementia, identifiable by neuropsychological assessment showing impairments with a great variety of cognitive tests. However, test scores are often colinear, largely because common cognitive components are involved in different tests; in spite of an apparent heterogeneity, it is still possible that a common cognitive component may be responsible for the deterioration shown in different tests in the preclinical phase. We studied the cognitive performances of 1159 elderly residents in the PAQUID (Personnes Agées quid) cohort, at a fixed lag time of 2 years before the clinical diagnosis of dementia. Seven neuropsychological tests were administered (Mini-Mental Status Examination, Benton Visual Retention Test, Wechsler Paired-Associates Test, Isaacs Set Test, Zazzo's Cancellation Task, Digit Symbol Substitution Test and Wechsler Similarities Test). Among the initially non-demented 1159 subjects, 25 developed a dementia 2 years later, of whom 16 were classified as cases of Alzheimer's disease. In order to dissect the multicolinearity of the tests we used a multivariate approach with principal component analysis (PCA). The patients' loading on each of the first four PCA factors were subsequently correlated with the risk of dementia and Alzheimer's disease 2 years later. The logistic regression with backward stepwise selected only the first factor as an independent predictor of dementia or Alzheimer's disease. Analysis shows that there are good reasons to suspect that the first PCA factor represents a general factor corresponding to aspects of control in the tasks used. Our results therefore seem to show that preclinical deficits in dementia and Alzheimer's disease reflect the deterioration of a general cognitive factor, which may be interpreted as the disturbance of central, control processes.

Two aspects of impaired consciousness in Alzheimer's disease

“…It was suggested that controlled processes (requiring attentional resources) are affected at an early stage while automatic processes are relatively more preserved (Jorm, 1986). The hypothesis of controlled processes impairment was explicitly explored in recent studies (Fabrigoule et al, 1998;Salthouse and Becker, 1998;Amieva et al, 2000). For example, Fabrigoule (1998) longitudinally studied cognitive performances in a large sample of 1,159 healthy elderly subjects.…”

“…Current features for dementia include a deterioration in cognitive functions, sufficient to impair daily living activities (APA, 1994). Neuropsychological studies have demonstrated that AD patients show impairment in controlled cognitive processes, while automatic activities may be more preserved (Fabrigoule et al, 1998). It is frequently observed that AD patients fail to consciously recollect information whereas they provide target memories in implicit conditions.…”

Specificity of inhibitory deficits in normal aging and Alzheimer's disease

“…We also expect a further and specific decrease of performance in AD patients (by comparison to healthy elderly subjects) on inhibitory tasks requiring controlled processes. Indeed, it is now well acknowledged that the various cognitive deficits presented by AD patients in the early stages of the disease are characterized by an impairment of controlled processes associated to a preservation of the automatic ones [1,38,87].…”

A basic study of declining visual cognitive skills using a position estimation task.

“…1 The results from this experiment shows evidence of this when the blind distance becomes wider. In this experiment, two interesting points were observed, one being the subject's ability to estimate the target more or less accurately in a blind area after memorizing the speed of the object.…”

“…While studies in areas of assessing were mainly concentrated on neuropsychological assessment measures which results varies across studies due to subjectivity, measuring the impairment directly in terms of units and numbers are not well studied and is difficult. 1 The purpose of this study was to investigate the decline in visual and cognitive abilities in young healthy individuals by comparing the results of two variables of the experiment namely; speed and blind distance. The cognitive function's outcome is a result of a higher intelligence in the working memory in the frontal lobe region.…”