| Intraindividual variability describes fluctuation or transient change in performance, and can be measured by repeated assessment of an ability or trait over a short period of time. Intraindividual variability in biological systems has been demonstrated to indicate systemic compromise (e.g., loss of homeostatic regulation). Consequently, one theory investigators have begun to research is whether intraindividual variability or fluctuation in cognitive performance may be an indicator of cognitive decline. Additionally, a second theory suggests that fluctuations in cognitive performance may be greater during periods of learning acquisition, with a corresponding reduction in variability following the acquisition phase. This study investigated intraindividual variability of cognition on measures of attention, processing speed, working memory, and episodic memory in older adults (over 65 years of age) with and without mild cognitive impairment (MCI), by assessing performance in these domains daily for 31 days. MCI may be a transitional stage between normal aging and dementia. In particular, the term amnestic MCI describes individuals with focal cognitive impairment in the memory domain; such impairment might foretell future Alzheimer's dementia. For this study, MCI is defined as list memory performance 1.5 standard deviations below age-appropriate norms, supplemented by subjective memory complaints and informant report of memory problems, as well as intact cognition in non-memory domains. Results revealed that older adults with amnestic MCI demonstrated a pattern of intraindividual variability and performance level that was consistent with patterns seen in previous studies of cognitively intact or demented individuals. Individuals with MCI demonstrated similar rates of practice-related gain over occasions as did the cognitively intact individuals. However, intraindividual variability was related inversely to performance, for most measures. MCI status was not consistently related to intraindividual variability across the cognitive battery studied. Interrelationships of performance gain slopes with degree of fluctuation did not provide clear evidence for either of the two theories regarding the role of intraindividual variability in practice-related gain or neurocognitive vulnerability. These findings provided evidence that the two types of intraindividual variability described by the current theories in the literature may co-occur in the MCI population. |
