From a Scientific American article titled:
At the end of three months, the reduced-calorie diet group showed a small reduction in body weight (by 2.4 kilograms), whereas the other two diet groups showed a slight increase in weight (by about one kilogram). There was, however, a highly significant (about 20 percent above baseline) improvement in the CR group’s ability to recall words they had on a list (called delayed recall), and they also made fewer errors. Their memory improvement tended to be correlated with reductions in blood insulin and markers of inflammation (C-reactive protein and TNF-alpha). Memory did not change in the other two diet groups.
So, if eating fewer calories is good for the brain, I suspect that there is an inverse corollary in there somewhere. . . One that explains my occasional inability to retain a list of three items for which my wife sent me to the store beyond the five minute drive to get there.