Blueberries: A 2012 study suggested that eating at least one serving of blueberries a week slowed cognitive decline by several years. One possible explanation as to why came from a 2013 study in mice, which found that berries might protect the brain by clearing toxic proteinsthat accumulate there.

Source: http://www.huffingtonpost.com/2014/07/12/blueberry-health-facts-benefits_n_5568690.html