There appears to be some evidence that brain training (cognitive stimulation) using computer-based memory training games may assist in the preservation of cognitive functioning in older adults, aged 65 or above, and might have some limited potential to help reduce dementia risk.
The following NHS Choices Behind the Headlines critical appraisal provides a due sense of perspective by discussing some potential limitations in this particular research.
Still no evidence brain training protects us against dementia. London: NHS Choices; Behind the Headlines, November 17th 2017.
This relates to:
Edwards, JD. Xu, H. [and] Clark, DO. [et al] (2016). Speed of processing training results in lower risk of dementia. Alzheimer’s and Dementia: Translational Research and Clinical Interventions. November 7th 2017. [Epub ahead of print].