A new review published in the May 2017 edition of Frontiers in Nutrition analyzed the evidence to date that flavanols (found in dark chocolate and cocoa, among other foods) may benefit human brain function. Flavanols are a form of flavonoids, plant-based substances that have anti-inflammatory and antioxidant effects. Here’s a sample of the findings:

• Short-term consumption may be helpful. For example, a 2011 study of young adults found that two hours after consuming dark chocolate (with high flavanol content), memory and reaction time were better than among those consuming white chocolate (with low flavanol content). However, other similar studies showed no benefit.
• Long-term consumption may be helpful. One 2014 study found that among adults ages 50 to 69, those taking a cocoa supplement with high flavanol content for three months had better performance on tests of memory than those assigned to take a low-flavanol cocoa supplement.
• Several studies demonstrated evidence of improved brain blood flow, oxygen levels, or nerve function as measured by imaging tests or tests of electrical activity in the brain after the consumption of cocoa drinks. But because these changes were not routinely associated with improved performance on cognitive tasks, it’s hard to connect the results directly to better brain function.

That is From Harvard’s Health Blog, in an article Your brain on chocolate by Robert H. Shmerling, MD, with  Link To Article Here and Link Full Study Here