I need the biggest brain I can realistically get, how big is it and why?
I've done a bit of research. I know we (humans) have big brains. We've even got big brains compared to our weight (encephalization ratio)!
Dolphins, elephants and whales have bigger brains, but they also have bigger neurons, so neuron density is lower. They're also noisier, so more redundancy is needed (and thus wasted neurons) compared to a smaller brain.
In my story, I want my main character to meet a giant biological brain, preferably in a suitably sized vat. I need to know how big of a brain I can realistically get.
Things I'm already considering are:
- Neurons are slow, so beyond a certain size the time delays will be too large (if it takes over a second to get signals from one end to the other, can there be meaningful computation? I don't think so.)
- There may be issues with cooling a big brain
- There may be overwhelming vascularization needs (or whatever artificial substitute for blood vessels), but I don't know how to even start putting numbers on that...
So please help me: How big can a brain conceivably be?