Cognitive impairment is a core feature of depression , common not only in symptomatic but also remitted states , and only partially responsive to common antidepressants . A history of depression is one of the most robust dementia risk factors, associated with approximately 80% higher risk of developing dementia in late life  and given its relatively high prevalence, may independently account for about 8% of dementia cases worldwide . Moreover, depression is one of the most common comorbidities in chronic diseases, may interfere with management and lead to poorer functional outcomes . Therefore, interventions that effectively target cognition alongside other symptoms in people with depression may have an important role in not only maintaining everyday function , but also in delaying or preventing cognitive decline and dementia [4, 8].
Computerised cognitive training (CCT) is a key component of cognitive remediation and has received increasing interest for targeting cognitive and functional outcomes in depression and a range of other mental disorders [7, 9]. CCT is different from other approaches by focusing on repeated and controlled practice on cognitively demanding tasks targeting one or more cognitive domains, as opposed to explicit learning of compensatory strategies [7, 9]. CCT is inherently safe, typically adaptive to individual needs, provides ongoing feedback and can be delivered inexpensively in a range of healthcare and community settings. Meta-analyses of randomised controlled trials (RCTs) investigating CCT by itself or in combination with other strategies have reported small-to-moderate effect sizes for not only cognition but also for psychosocial and functional outcomes in schizophrenia [10, 11], psychosis  and mild cognitive impairment . However, effect size estimates are often heterogeneous and vary across populations, outcomes or intervention design factors such as training content, dose and supervision [10, 11, 14].
The efficacy of CCT in people with depression has been previously investigated in two systematic reviews with meta-analysis. Motter and colleagues  reported moderate effect sizes on measures of symptom severity, daily functioning and attention, as well as large effect sizes on working memory and global cognition. Effect sizes for executive functions and verbal memory were small and imprecise. Although the review inclusion criteria were specified to RCTs of CCT, at least three of the nine included studies were not randomised trials [16–18] and one provided memory strategy training rather than CCT . More recently, Chan and colleagues  investigated the effects of different cognitive interventions on depression outcomes in older people with mild cognitive impairment or dementia. The review included seven CCT studies, which reported large and statistically significant effect size on depressive symptoms. However, none of the included studies specifically targeted people with depression, and mean baseline scores were below the cut-off for depressive disorder in all studies.
Therefore, while results of preliminary meta-analyses as well as those in other populations are encouraging, the potential of CCT as an effective intervention for cognition and function in people with depression has yet to be systematically and robustly evaluated. Moreover, investigations of the extent to which design factors such as population characteristics, concurrent pharmacological or psychological treatments, intervention strategies, control comparisons and study quality may relate to clinical outcomes are required in order to inform clinical guidelines .
The aim of this review is to evaluate the efficacy of CCT on cognitive, mood, psychosocial and functional outcomes in adults with depression. Specifically, we aim to:
Investigate the efficacy of CCT on cognitive, mood, psychosocial outcomes and daily function in comparison to active or passive control.
Examine study and intervention design factors that could moderate CCT effects across studies in each domain.
Evaluate the strength and quality of the evidence for CCT in depression.
Suggest recommendations for future research and practice in the field.