Dear Jerry,
You ask about the brain and death and posit a materialist argument by Kinbote. But Kinbote is a religious zealot! On the other hand you are right that Shade seems to have a spiritual experience during his fits. I seem to recall something similar in Pnin.
Only death however completely stops the brain and the attacks that Shade suffers do not kill him - - he even survives the last one for a while and only at some later point (when he is "shot") does Kinbote become the lone survivor once Gradus is safely locked up in jail. And only sometime on or after October 19 when the preface is signed by Kinbote does death by suicide come in a strange motel room - - beyond the novel itself although foreseen by both Kinbote and Shade.
If Zembla is a brain, it is the brain of a repressed homoerotic - - that could explain its shape (recall that Shade is himself misshapen) and asymmetry. Both Shade and Kinbote do marry after all, and even Kinbote unwillingly admits that the only person he really loved is Disa. So the homosexual and heterosexual aspects of both exist, but never in balance.
And the fountain wasn't linked with Maud that I can recall, but with Shade and a "Mrs Z." I think.
By the way Maud and the Countess de Fyler both die shattered in 1950 and the Countess's "Charles take take flower flower flower" message seems to be an echo of Maud's posthumous rant, perhaps from the time that Shade says "she still could speak"?
Carolyn