Neuroimaging Outcomes in Studies of Cognitive Training in Mild Cognitive Impairment and Early Alzheimer's Disease: A Systematic Review

Background Cognitive training (CT) has demonstrated some benefits to cognitive and psychosocial function in mild cognitive impairment (MCI) and early dementia, but the certainty related to those findings remains unclear. Therefore, understanding the mechanisms by which CT improves cognitive functioning may help to understand the relationships between CT and cognitive function. The purpose of this review was to identify the evidence for neuroimaging outcomes in studies of CT in MCI and early Alzheimer's disease (AD). Methods Medline, Embase, Web of Science, PsycINFO, CINAHL, and The Cochrane Library were searched with a predefined search strategy, which yielded 1778 articles. Studies were suitable for inclusion where a CT program was used in patients with MCI or AD, with a structural or functional magnetic resonance imaging (MRI) outcome. Studies were assessed for quality using the Downs and Black criteria. Results A total of 19 studies met the inclusion criteria. Quality of the included studies was variable and there was significant heterogeneity for studies included in this review. Task activation was generally increased post-training, but functional connectivity was both increased and decreased after training. Results varied by diagnosis, type of CT program, and brain networks examined. No effects were seen on hippocampal volumes post-training, but cortical thickening and increased grey matter volumes were demonstrated. Conclusions CT resulted in variable functional and structural changes in dementia, and conclusions are limited by heterogeneity and study quality. Larger, more robust studies are required to correlate these findings with clinical benefits from CT.