WTF is a collective brain? That sounds like the antithesis of creativity.
Shortest possible answer... A collective brain is what you'd have if human communication prior to the incident associated with the tower of Babel were basically telepathic (which is one interpretation of Julian Jayne's findings), if Jaynes were correct in thinking that consciousness as we know it did not exist 4000 years ago, and if consciousness in those days were basically general rather than individual.
Michael Crichton wrote a science fiction novel called “Prey”. The plot concerns a research lab develops tiny nano-machines capable of replicating animate objects capable of intelligent behavior when many of them swarm together. It’s a step up from the idea that certain insects, like bees or termites, that seem just as stupid as any other insect when acting alone, are capable of building complex structures and organized colonies when interacting in large numbers.
I Googled “collective brain”. Computer software people seem to be trying to simulate this idea.
The Democrat Party?
Maybe a better name might be the “integrated brain”. This seems to be the idea of Jaynes, for one. I was quite impressed by his book, although I couldn’t agree with his conclusions. Even so, the scope of his thinking impressed me. After all, if you believe that there was a natural origin of human consciousness, you must face the question how it occurred.
I will say that whatever the natural history of consciousness may be, its mere existence is beyond the ken of materialist philosophy.