I've heard from someone that raises parrots that they can get as smart as
a five-year-old.  I imagine that this is along only one or two of the many
axes of intelligence, though.
I assume that by "brain cells" you mean neurons?  I think humans can
regrow non-neuronal brain cells (in adulthood).
Kennita
Kennita Watson    | The bond that links your true family is not one of blood,
kwatson@netcom.com| but of respect and joy in each other's life.   Rarely do
                  | members of the same family grow up under the same roof.
                  |                            -- Richard Bach, _Illusions_