Cognitive and memory training in adults at risk of dementia: A Systematic Review

BMC Geriatrics Cognitive and memory training in adults at risk of dementia: A Systematic Review Nicola J Gates 0 Perminder S Sachdev 0 Maria A Fiatarone Singh Michael Valenzuela 0 0 School of Psychiatry, University of New South Wales , RandwickNSW 2031 , Australia Background: Effective non-pharmacological cognitive interventions to prevent Alzheimer's dementia or slow its progression are an urgent international priority. The aim of this review was to evaluate cognitive training trials in individuals with mild cognitive impairment (MCI), and evaluate the efficacy of training in memory strategies or cognitive exercises to determine if cognitive training could benefit individuals at risk of developing dementia. Methods: A systematic review of eligible trials was undertaken, followed by effect size analysis. Cognitive training was differentiated from other cognitive interventions not meeting generally accepted definitions, and included both cognitive exercises and memory strategies. Results: Ten studies enrolling a total of 305 subjects met criteria for cognitive training in MCI. Only five of the studies were randomized controlled trials. Meta-analysis was not considered appropriate due to the heterogeneity of interventions. Moderate effects on memory outcomes were identified in seven trials. Cognitive exercises (relative effect sizes ranged from .10 to 1.21) may lead to greater benefits than memory strategies (.88 to -1.18) on memory. Conclusions: Previous conclusions of a lack of efficacy for cognitive training in MCI may have been influenced by not clearly defining the intervention. Our systematic review found that cognitive exercises can produce moderateto-large beneficial effects on memory-related outcomes. However, the number of high quality RCTs remains low, and so further trials must be a priority. Several suggestions for the better design of cognitive training trials are provided. - Background Development of preventative strategies for Alzheimers dementia (AD) is an international priority, with prevalence rates projected to increase by over 75% in the next quarter of a century [1]. One approach to reduce the prevalence of AD is to develop strategies to delay its onset in healthy individuals or those at risk of developing dementia. Prospective cohort studies have found that participation in mentally-stimulating activities is associated with a lower incidence of AD [2] and even late-life mental activity exhibits a dose-dependent inverse relationship with dementia risk, independent of early life experiences [3]. Consequently, it is possible that participation in complex mental activities at older age may offer protection from cognitive decline and hence mitigate dementia risk. Cognitive training provides structured practice of complex mental activity in order to enhance cognitive function [4], and has attracted intense public, commercial and scientific interest. Unfortunately, cognitive training interventions have been frequently mislabelled or conflated with other therapies, despite important theoretical distinctions between compensatory cognitive rehabilitation, general cognitive stimulation and cognitive training [5-7]. For example, the non-specific umbrella terms cognitive intervention [8], cognitive enrichment [9] and cognitive rehabilitation have been applied to multidomain cognitive training [10-12] as well as training in memory strategies [13]. Cognitive stimulation has been used to refer to interventions ranging from generic topical discussions [14], executive exercises and memory strategy training [15]. Given the confusion of terms, an operational definition has been advanced which delineates cognitive training from other interventions [16]: 1) repeated practice, 2) on problem activities, 3) using standardized tasks, and 4) that target specified cognitive domains. Cognitive training can be further distinguished to include training in applied memory strategies versus repetitive cognitive exercises [7]. Training in memory strategies involves the instruction and practice of techniques to minimize memory impairment and enhance performance, and involves learning and practicing strategies such as the method of loci, mnemonics, and visual imagery [17,18]. In contrast, cognitive exercise requires the repeated practice of targeted cognitive abilities in a repetitions-sessions format analogous to reps-sets regimes in physical resistance training: users typically carry out a number of iterations of a cognitive task in one session, then continue to new tasks in the next session, and eventually return to further train the original task at a harder level in future sessions (i.e., staircase design). Recently, several software applications have been developed that implement cognitive exercises on computer [19,20]. Although cognitive exercises and memory strategies are structurally distinct, they have often been analysed together. A Cochrane review of 32 training trials up to the year 2007, concluded that none of the effects could be attributed specifically to cognitive training, however, only memory training data from 24 trials were pooled for analysis, and the analysis did not include results from cognitive exercise trials of problem solving and speed of information processing [4]. Similarly a review of memory strategy training in healthy and mild cognitive impairment (MCI) individuals [18] combined results from two trials of cognitive exercises [11,19] with 22 trials of memory strategy training and found no specific effects of training. Furthermore, mixed results were also obtained in a systematic review of cognitive interventions in MCI which included training in both memory strategies and cognitive exercises [21]. In addition, many of the trials included uncontrolled interventions such as use of external memory aids or relaxation therapy [22]. Prior reviews have therefore not appropriately distinguished between types of cognitive training, potentially obscuring clinically-relevant effects. Furthermore, a lack of differentiation between cognitive exercises and training in memory strategies, and the inclusion of multiple other therapies with cognitive training, may have also contributed to mixed findings. By contrast, a meta-analysis of longitudinal RCTs of cognitive training (as defined here) in cognitively healthy adults demonstrated efficacy on primary cognitive outcomes [23]. However, whether operationally-defined cognitive training can be as effective at slowing the rate of cognitive decline after clinical signs are apparent is not clear. MCI is a diagnostic term applied to those individuals with high risk of developing dementia and in the intermediate stage between normal cognitive function and dementia [24,25]. MCI increases the risk for dementia, with diagnosed individuals progressing at rates of 12-15% per year compared to 1-2% of the general population [26]. Cognitive training at this preclinical stage may potentially prevent or delay disease onset, re (...truncated)