Abstract: We identified eight RCTs with a total of 1183 participants. The duration of the interventions ranged from 12 to 26 weeks; in five trials, the duration of intervention was 12 or 13 weeks. The included studies had moderate risk of bias, and the overall quality of evidence was low or very low for all outcomes. We compared CCT first against active control interventions, such as watching educational videos. Negative SMDs favour CCT over control. Trial results suggest slight improvement in global cognitive function at the end of the intervention period (12 weeks) (standardised mean difference (SMD) -0.31, 95% confidence interval (CI) -0.57 to -0.05; 232 participants; 2 studies; low-quality evidence). One of these trials also assessed global cognitive function 12 months after the end of the intervention; this trial provided no clear evidence of a persistent effect (SMD -0.21, 95% CI -0.66 to 0.24; 77 participants; 1 study; low-quality evidence). CCT may result in little or no difference at the end of the intervention period in episodic memory (12 to 17 weeks) (SMD 0.06, 95% CI -0.14 to 0.26; 439 participants; 4 studies; low-quality evidence) or working memory (12 to 16 weeks) (SMD -0.17, 95% CI -0.36 to 0.02; 392 participants; 3 studies; low-quality evidence). Because of the very low quality of the evidence, we are very uncertain about the effects of CCT on speed of processing and executive function. We also compared CCT to inactive control (no interventions). We found no data on our primary outcome of global cognitive function. At the end of the intervention, CCT may lead to slight improvement in episodic memory (6 months) (mean difference (MD) in Rivermead Behavioural Memory Test (RBMT) -0.90 points, 95% confidence interval (CI) -1.73 to -0.07; 150 participants; 1 study; low-quality evidence) but can have little or no effect on executive function (12 weeks to 6 months) (SMD -0.08, 95% CI -0.31 to 0.15; 292 participants; 2 studies; low-quality evidence), working memory (16 weeks) (MD -0.08, 95% CI -0.43 to 0.27; 60 participants; 1 study; low-quality evidence), or verbal fluency (6 months) (MD -0.11, 95% CI -1.58 to 1.36; 150 participants; 1 study; low-quality evidence). We could not determine any effects on speed of processing because the evidence was of very low quality. We found no evidence on quality of life, activities of daily living, or adverse effects in either comparison. We found low-quality evidence suggesting that immediately after completion of the intervention, small benefits of CCT may be seen for global cognitive function when compared with active controls, and for episodic memory when compared with an inactive control. These benefits are of uncertain clinical importance. We found no evidence that the effect on global cognitive function persisted 12 months later. Our confidence in the results was low, reflecting the overall quality of the evidence. In five of the eight trials, the duration of the intervention was just three months. The possibility that more extensive training could yield larger benefit remains to be more fully explored. We found substantial literature on cognitive training, and collating all available scientific information posed problems. Duration of treatment may not be the best way to categorise interventions for inclusion. As the primary interest of older people and of guideline writers and policymakers involves sustained cognitive benefit, an alternative would be to categorise by length of follow-up after selecting studies that assess longer-term effects.

Plain-language summary: We found eight trials with a total of 1183 participants to include in the review. Five trials provided CCT for three months, two for four months, and one for six months. We compared CCT with other activities, such as watching educational videos, and with no activity. We looked for effects on overall cognitive function and on specific cognitive functions, such as memory and thinking speed. All of the included studies had some design problems, which could have biased the results. Overall, we thought the quality of the evidence that we found was low or very low. This means we cannot be confident in the results, and that future research might well find something different. CCT may slightly improve overall cognitive function after 12 weeks of training; however, we found no evidence of a persistent effect 12 months after the intervention. We were unable to comment or found little evidence that CCT when compared with other activities may have a relevant effect on most of the specific cognitive functions that we examined. The longest trial found that compared to doing nothing, completing six months of CCT may have had a beneficial effect on memory. None of the included trials reported effects of cognitive training on quality of life or on daily activities, and none reported harmful effects of training. Compared to other activities, CCT may lead to slightly better overall cognitive function at the end of 12 weeks of training, but we found no evidence that the effect persists a year later. Compared to doing nothing, CCT may slightly improve memory at the end of six months of training. Although we excluded trials with less than 12 weeks of training, the trials that we included were still quite short for examining long-term effects as people age. A limitation of our review is that we did not include some trials with shorter training periods that did look for long-lasting effects, so it is possible that we missed some useful evidence. Many published studies have looked at computer training. Making sense of this substantial literature is difficult. It may be more helpful in the future to categorise trials by the duration of effects of training rather than by the duration of the training itself.