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https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2821441/
http://n.neurology.org/content/75/11/990
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3439198/
http://newsroom.ucla.edu/releases/ucla-memory-fitness-education-213606
https://www.medscape.com/viewarticle/749031