The Technium: Brains of White Matter

[Rynn]

I think that beyond a certain brain size, human-style unified consciousness becomes impossible, as the number of connections required between nodes would become unworkable, regardless of what technology was used.

Adjusting the clock rates of the various components should do it. If the systems for coordination are running faster than everything else then an entity can grow in size whilst maintaining unity. As with many aspects of technology in OA this is a trade off.