Reaction times and performance variability in normal aging, mild cognitive impairment and Alzheimer's disease.

The aim of this study was to evaluate whether reaction times (RT) and performance variability are potential markers for the early detection of Alzheimers disease (AD). Cognitively healthy elderly (n=218), persons with amnestic MCI (a-MCI) (n=29) and patients with AD (n=50) were examined with RT tasks, subdividing RT into a decision and a movement component. Inter-individual variability is greater for persons with cognitive deterioration than for cognitively healthy elderly. AD patients were slower and showed more intra-individual variability than cognitively healthy elderly and persons with a-MCI. The slowing in AD affects both the cognitive and the motor component, while performance variability mainly affects the cognitive component. Persons with a-MCI are consistently slower and show more intra-individual variability than cognitively healthy elderly, although not all differences reached statistical significance. Mainly the cognitive component of the RT is affected in a-MCI. Intra-individual variability and RT of the complex tasks are the best predictors for respectively a-MCI and AD status. We conclude that performance variability can be regarded as a useful preclinical marker for AD.