A Cochrane review included 36 RCTs. A total of 24 trials were pooled including 2229 participants: 767 healthy older adults and 34 participants with mild cognitive impairment (from 3 trials), 442 no contact controls and 986 controls with alternative treatments (active controls) were included. An estimated mean age was 70 years. Interventions were grouped into cognitive domains (such as memory, executive function, attention and speed) and then pooled to create ability subgroups within the domains. Most of the studies included focus on memory training interventions, and very few on speed improvements or training of executive functioning. For healthy older adults, immediate and delayed verbal recall improved significantly (p<0.05) through training compared to a no-treatment control condition. For individuals with mild cognitive impairment, significant training gains were obtained for treatment compared to no contact control in immediate (p=0.04) recall and delayed recall (p=0.05). This improvement was not specific, however, as it did not exceed the improvement observed in the active control condition.
Comment: The quality of the evidence is downgraded by study quality (inadequate allocation concealment, lack of blinding), inconsistency (heterogeneity in interventions and outcomes) and indirectness of evidence (differences in patient and studied interventions).