Cognitive Reserve in Young and Old Healthy Subjects: Differences and Similarities in a Testing-the-Limits Paradigm with DSST

Abstract

Cognitive reserve (CR) is understood as capacity to cope with challenging conditions, e.g. after brain injury or in states of brain dysfunction, or age-related cognitive decline. CR in elderly subjects has attracted much research interest, but differences between healthy older and younger subjects have not been addressed in detail hitherto. Usually, one-time standard individual assessments are used to characterise CR. Here we observe CR as individual improvement in cognitive performance (gain) in a complex testing-the-limits paradigm, the digit symbol substitution test (DSST), with 10 repeated measurements, in 140 younger (20–30 yrs) and 140 older (57–74 yrs) healthy subjects. In addition, we assessed attention, memory and executive function, and mood and personality traits as potential influence factors for CR. We found that both, younger and older subjects showed significant gains, which were significantly correlated with speed of information processing, verbal short-term memory and visual problem solving in the older group only. Gender, personality traits and mood did not significantly influence gains in either group. Surprisingly about half of the older subjects performed at the level of the younger group, suggesting that interindividual differences in CR are possibly age-independent. We propose that these findings may also be understood as indication that one-time standard individual measurements do not allow assessment of CR, and that the use of DSST in a testing-the-limits paradigm is a valuable assessment method for CR in young and elderly subjects.

Cognitive reserve in the healthy elderly: cognitive and psychological factors

“…Overall, the present results are consistent with those of our previous study [16] and favor the evidence that activation of cognitive resources is well preserved in the healthy elderly, notwithstanding individual differences in performance gains. In this study, performance gain in the DSST testing-the-limits paradigm was 15.53 items (SD = 6.03), as compared to 18.94 items (SD = 7.30) in our earlier study [16].…”

“…In this study, performance gain in the DSST testing-the-limits paradigm was 15.53 items (SD = 6.03), as compared to 18.94 items (SD = 7.30) in our earlier study [16]. Interestingly, the younger group (20-30 years) in our earlier study [16] showed a higher gain (25.52), but variability was in a similar range (SD = 10.10).…”

“…In this study, performance gain in the DSST testing-the-limits paradigm was 15.53 items (SD = 6.03), as compared to 18.94 items (SD = 7.30) in our earlier study [16]. Interestingly, the younger group (20-30 years) in our earlier study [16] showed a higher gain (25.52), but variability was in a similar range (SD = 10.10). This supports the idea that CR is not a quality of older age alone [32], and that interindividual variability is already apparent at earlier ages; therefore, aging is not the main or only determinant of CR variability in older age.…”

“…Calculation of indexes of CR: Given the usefulness of simple gain scores [30], we used the following formula as an index for CR [16]:…”

“…The use of the Digit Symbol Substitution Test (DSST), a multi-tasking cognitive measure [15], in a testing-the-limits paradigm with systematic repetition offers a way to assess CR in a dynamic way. In our recent study that contrasted 140 younger with 140 older healthy subjects, all of whom had a similar level of education [16], we used such a paradigm to assess CR. The main outcome of that study was that systematic practice with DSST leads to significant gains in both age groups.…”