Intraindividual variability as a marker of neurological dysfunction : a comparison of Alzheimer's disease and Parkinson's disease.
Date
2002
Authors
Burton, Catherine Louisa
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
The study of intraindividual variability involves measuring fluctuations in an individual's performance across short intervals of time (e.g., minutes, day, weeks). Several researchers have suggested that intraindividual variability may be a behavioural marker of compromised neurobiological mechanisms associated with aging, disease, and injury (Bruhn & Parsons, 1977; Li & Lindenberger, 1999). For example, older adults and individuals with certain neurological conditions, such as traumatic brain injuries, epilepsy, and Alzheimer's disease (AD), have been shown to demonstrate greater intraindividual variability in cognitive and/or physical functioning than younger adults or healthy controls (Anstey, 1999; Bruhn & Parsons, 1977; Ferrandez, Durup, & Farioli, 1996; Hultsch, MacDonald, Hunter, Levy-Bencheton, & Strauss, 2000; Strauss, MacDonald, Hunter, Moll, & Hultsch, in press). The present study sought to investigate whether intraindividual variability is associated with general nervous system compromise or certain types of neurological disturbances by comparing 3 groups of older adults: healthy adults, and adults with either AD or Parkinson's disease (PD), two neurodegenerative disorders with differing neuropathology. Following an intake session, participants were assessed weekly on 4 separate occasions on a battery of cognitive (i.e., reaction-time, episodic memory), physical (i.e., grip strength, finger dexterity, blood pressure, pulse, respiratory functioning, gait), and affective/stress measures (i.e., affect, stress, pain, perceived competence, locus of control). Results indicated that on measures of cognitive functioning, the AD group demonstrated greater intraindividual variability in latency than the PD group, which in tum demonstrated greater variability than the healthy group. On a measure of left finger dexterity, the AD group was significantly more variable than both the healthy and PD groups. However, intraindividual variability tended to be significantly correlated with severity of impairment and controlling for group differences in severity of impairment eliminated these significant group differences in intraindividual variability. Correlational analyses indicated that intraindividual variability was also related to variability on other tasks, as well as to level of performance on other tasks, particularly within the cognitive domain. These findings provide further support for an association between intraindividual variability and neurological dysfunction, in particular suggesting that intraindividual variability may be primarily associated with severity of neurological dysfunction, regardless of the nature of neurological compromise.