The reviewed research first mapped out the precise brain location for age-related dysfunction using functional MRI. The researchers then had 50-69 year old participants either consume a high or a low cocoa flavanol diet for 3 months(Brickman AM,et al. 2014).
The results showed that a high flavanol diet was found to enhance dentate gurus function, that is the function related to memory dysfunction, when measured with functional MRI and cognitive testing.
To increase your cocoa flavanol intake you can either eat some dark chocolate with a high flavanol content or drink some cocoa. Dark chocolate and cocoa are bitter; for that reason sugar is added of course, so be sure to watch your sugar levels with chocolate. The more bitter you can handle the better.
Brickman AM, Khan UA, Provenzano FA, Yeung LK, Suzuki W, Schroeter H, Wall M, Sloan RP, Small SA. Enhancing dentate gyrus function with dietary flavanols improves cognition in older adults. Nat Neurosci. 2014 Dec;17(12):1798-803. doi: 10.1038/nn.3850. Epub 2014 Oct 26.