Objectives: Epidemiological and preclinical studies suggest that mental activity levels may alter dementia risk. Clinical trials are now beginning to address the key issues of persistence of effect over extended follow-up and transfer of effect to nontrained domains. The aim of this report was to therefore systematically review results from clinical trials, which have examined the effect of cognitive exercise on longitudinal cognitive performance in healthy elderly individuals.
Methods: MEDLINE, PubMed, and key references were used to generate an initial list of relevant studies (N = 54). These were reviewed to identify randomized controlled trials, which tested the effect of a discrete cognitive exercise training regime on longitudinal (>3 months) posttraining neuropsychological performance in healthy older adults. Seven RCTs met entry criteria. Prechange and postchange scores were integrated using a random effects weighted mean difference (WMD) meta-analytic approach (Review Manager Version 4.2).
Results: A strong effect size was observed for cognitive exercise interventions compared with wait-and-see control conditions (WMD = 1.07, CI: 0.32-1.83, z = 2.78, N = 7, p = 0.006, N = 3,194). RCTs with follow-up greater than 2 years did not appear to produce lower effect size estimates than those with less extended follow-up. Quality of reporting of trials was in general low.
Conclusion: Cognitive exercise training in healthy older individuals produces strong and persistent protective effects on longitudinal neuropsychological performance. Transfer of these effects to dementia-relevant domains such as general cognition and daily functioning has also been reported in some studies. Importantly, cognitive exercise has yet to be shown to prevent incident dementia in an appropriately designed trial and this is now an international priority.