The hippocampus is a key part of the brain involved in forming and retrieving memories. This is the only part of the brain where new neurons are formed in response to environmental events. A recent study of food-storing birds shows that their hippocampi (plural, for each half of the brain has one) undergo an increase in size due to formation of new neurons. A bigger hippocampus enhances the ability of birds to find places to cache their food, and later, remember where they are. During late fall and in the winter, the hippocampi are larger, and during spring and summer, when food storage is less important, they become smaller.
To move from birds to man, there is now solid evidence that physical and mental exercise can increase hippocampus size. This is especially important in older individuals, for it provides a way to prevent age-related shrinkage of the hippocampus, limit memory loss and enhance thinking. (Sherry and Hoshooley, Philosophical Transactions of the Royal Society B: Biological Sciences, Feb. 15, 2010; Erickson et al, Proc. of the National Academy of Sciences, Feb. 15, 2011)