The Baldur's Gate 3 brain puzzle is one of the harder challenges you're likely to find while exploring the game. Towards the end of act two, you'll find yourself back in the dank and dark depths of Mind Flayer Colony, and if you do a little exploring into the Necrotic Lab, you'll likely locate a console and a locked door. When you try to activate the console, it'll project a neural map of a brain you have to connect up.
The puzzle is basically a fancy connect the dots, but if you're willing to take the time—or just use our solution—you can get yourself a new brain to talk to in the nearby Mind Archive machine, and a very strong condition that'll give you advantage on future rolls. That said, here's how to solve the Baldur's Gate 3 brain puzzle.
How to solve the brain node puzzle
Once you activate the console, it's easy to get the general gist of the puzzle. You need to connect the four coloured centres of the brain: Speed, Emotion, Memory, and Reason, to their corresponding centres on the opposite side of a web of Neural Nodes. You do this by clicking a centre, and then clicking the node you want to connect it to. Simple, right?
Well, the problem is that no two centres can share a node, meaning they each have to have their own individual path to the other side, weaving in between each other, but never crossing over at the same node. It's kind of hard to describe exactly how to solve this puzzle, but the best way is to work from the completed birds-eye view image I've included above and complete one path at a time. Just hit O to view the puzzle from above for ease.
Once it's solved, a door will open revealing the Mind Flayer monument from the intro to the game, as well as the Waking Mind. If you haven't found the Mind Archive machine in the Necrotic Lab, it's very close to where the puzzle is. Slot the brain in and you'll find yourself talking to a Githzerai who requests you purge their brain in exchange for a boon. If you do this, you get the Githzerai Mind Barrier condition, which gives you a pretty handy advantage on all intelligence saving throws.