Magic conveniently "explains away" many things associated with shapeshifting, but in the course of some of my fiction writing, I endeavor to include some slightly more plausible explanations when possible.

One such aspect I've not been able to create a satisfactory explanation for is how a shapeshifter might retain most or all of their cognitive ability and memory as an animal with a much smaller or different brain structure.

One of my ideas is that the retention of such mental faculties is time-limited. The longer the shifter spends in a form, the more at risk he is to lose memories, etc. This introduces a risk factor which is sometimes good, for example, to give the protagonist an obstacle or limitation.

However in a different scenario, it would be useful to have a somewhat believable method by which a shapeshifter could effectively process and remember information—as a tiny mammal or bird—compared to his or her human brain. What sort of ways might this be explained?