# Big Brains Needed

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:

1. 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.)
2. There may be issues with cooling a big brain
3. 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?

• Umm, that's not how that works , elephants , dolphins and whale don't have bigger neurons , they have WAY more than human beings , it is only that humans have more neurons in their cerebral cortex, 13 billion to be precise. And since neuron counting is so much more precise at measuring intelligence than measuring brain to body mass ratio , and since their are so many things wrong with measuring brain to body mass ratios to measure intelligence ( for instance , elephants are vastly more intelligent than mice , but their ratio is 1/250 , where as the mouse's is 1/40 ) I'd go with neuron counting
– user15036
Feb 26 '16 at 13:49
• @TheoclesofSaturn, I think you haven't done your research. compared to rodents, and probably to whales and elephants as well, the human brain is built according to the very economical, space-saving scaling rules That's not to say that some animals don't have more neurons overall -- just many fewer than sheer size or weight would make you think. Feb 26 '16 at 14:28
• And, being so tightly packed humans do in fact have more neurons than an african elephant. Feb 26 '16 at 14:35
• Wikipedia? How about this - ncbi.nlm.nih.gov/pubmed/24971054 - anyone can make or change a Wikipedia article, so its fairly bad in the information source department, and if you finish that article , it refutes that claim
– user15036
Feb 27 '16 at 2:19
• At the risk of opening a can of worms that only I enjoy to eat... what are brains, anyway? Sep 14 '16 at 20:24

As big as you like. If you're designing it as opposed to evolving it then there realistically is no limit.

You would need to feed nutrients and oxygen in and out of the brain somehow but that can be done just by running pipes through it and having regularly spaced analogues for all the important things like hearts, lungs, kidneys, etc.

In the same way as our super-computer are actually thousands of smaller processors networked together you can build a "brain unit" which is a big organic neural network and the life support it needs.

You then connect these units together into a massive network allowing them to wire into each other at the connections like giant blocks of Lego. The plumbing to get supplies in and waste out could get interesting but the actual size would be virtually unlimited.

You'd also want to distribute inputs and outputs across the entire brain as well if you wanted it to actually do something instead of just sitting there and looking gooey.

So you might get a "brain block" the size of a human brain. You then put 9 of them together into a "brain cube", 9 of those together into a "superbrain" (each with 81 times as many neurons as a human), 9 of those together into a "megabrain", and so on.

Note that you most likely wouldn't (unless you wanted to) get a "brain in a vat" scenario like this. Each would be a metal cube apart from the connections between brains. Those could be electronic (less messy, easy to change cubes out, harder for disease to spread, etc) or actually involve opening parts of the cube up and letting the brains directly wire into each other.

• A transparent plastic cube, I would have thought. No point collecting hundreds of brains unless you're going to show them off. Feb 25 '16 at 15:41