Here's more research that a heart healthy diet is also good for the brain. According to a recent study published online on May 18, 2012 in the Annals of Neurology, eating "good" fats was associated with less cognitive decline over a four-year period.
This study involved 6,183 women over the age of 65 who were evaluated over a four-year time frame. They reported their diet to researchers and were tested several times throughout the study to assess their cognitive functioning.
Participants whose diet consisted of more monounsaturated fat (or "good" fat), such as olive oil, nuts or seeds, showed better memory and overall cognitive functioning over four years than those whose diets contained more "bad" fat, such as the saturated fat contained in butter, cheese and red meats. The women who ate more "bad" fat demonstrated a bigger cognitive decline throughout the study.
Research consistently has demonstrated that eating right, exercising, and staying mentally active can reduce the risk to develop Alzheimer's or another dementia. So, while scientists continue to work on isolating the causes of Alzheimer's, knowing how to reduce the risk plays a key role in the fight against Alzheimer's.
Also, here's more research on diet and its effect on cognitive functioning.