The effects of aerobic exercise on the structure and function of DMN-related brain regions: a systematic review

Physical activity may play a role in both the prevention and slowing of brain volume loss and may be beneficial in terms of improving the functional connectivity of brain regions. But much less is known about the potential benefit of aerobic exercise for the structure and function of the default mode network (DMN) brain regions. This systematic review examines the effects of aerobic exercise on the structure and function of DMN brain regions in human adulthood. Seven electronic databases were searched for prospective controlled studies published up to April 2015. The quality of the selected studies was evaluated with the Cochrane Collaboration's tool for assessing the risk of bias. RevMan 5.3 software was applied for data analysis. Finally, 14 studies with 631 participants were identified. Meta-analysis revealed that aerobic exercise could significantly increase right hippocampal volume (SMD = 0.26, 95% CI 0.01-0.51, p = 0.04, I² = 7%, 4 studies), and trends of similar effects were observed in the total (SMD = 0.12, 95% CI -0.17 to 0.41, p = 0.43, I² = 0%, 5 studies), left (SMD = 0.12, 95% CI -0.13 to 0.37, p = 0.33, I² = 14%, 4 studies), left anterior (SMD = 0.12, 95% CI -0.16 to 0.40, p = 0.41, I² = 74%, 2 studies) and right anterior (SMD = 0.10, 95% CI -0.17 to 0.38, p = 0.46, I² = 76%, 4 studies) hippocampal volumes compared to the no-exercise interventions. A few studies reported that relative to no-exercise interventions, aerobic exercise could significantly decrease the atrophy of the medial temporal lobe, slow the anterior cingulate cortex (ACC) volume loss, increase functional connectivity within the hippocampus and improve signal activation in the cingulate gyrus and ACC. The current review suggests that aerobic exercise may have positive effects on the right hippocampus and potentially beneficial effects on the overall and other parts of the hippocampus, the cingulate cortex and the medial temporal areas of the DMN. Moreover, aerobic exercise may increase functional connectivity or activation in the hippocampus, cingulate cortex and parahippocampal gyrus regions of the DMN. However, considering the quantity and limitations of the included studies, the conclusion could not be drawn so far. Additional randomized controlled trials (RCTs) with rigorous designs and longer intervention periods are needed in the future.