_Declarative memory involves the hippocampus, a bean shaped area that is also involved in orientation.
In a famous study of London taxi drivers, who have to negotiate a tangled maze of streets on a daily basis, it was found that they had all developed an unusually large right posterior hippocampus. Math is also correlated with such navigational ability, and experts (as opposed to novices) use the hippocampus when manipulating three dimensional objects in their heads. On the flip side, children with very low birth weight not only have smaller than average hippocampi but significant math deficits as well.
Apparently, navigational space and theoretical space are much the same from the brain's standpoint.
Playing games that grow the hippocampus should therefore benefit not only memory, but math and abstract thinking as well.