A model of executive functions in very old community dwellers: evidence from The Sydney Older Persons Study.

Executive functions (EF) are generally described as showing greater sensitivity to ageing compared to other cognitive domains. Numerous pitfalls exist in the measurement of EF due to loose definitions and lack of agreement on these concepts and uncertainty about the constructs being measured. To this date, the validity of EF constructs has not been examined in the old-old population. Performance of 122 randomly selected community dwellers aged between 81 and 97 years on nine EF tasks (seven of which commonly used in clinical practice) was examined. Factor analytic procedures using structural equation modelling (SEM) failed to satisfactorily explain the data according to four a priori models, the first two models reflecting two major constructs commonly found in current models of EF ("set" and "switch"), the last two reflecting task requirements. The best measure for each task was extracted using statistically driven analyses and further SEM revealed an orthogonal two-factor model which provided a good fit of the data, explaining between 8% and 25% of the total variance. This model can be interpreted in terms of reactive and spontaneous flexibility as proposed by Eslinger and Grattan (1993), with the first factor reflecting internally driven strategies and the second environment dependent strategies. Furthermore, these findings also suggest that: (a) unique tasks of EF may not be applicable to all age groups due to individual experience and changes in strategies; and (b) current clinical instruments may be inadequate to measure very specific aspects of the complex construct of EF.