Why not to grow human cortical brain tissue and train it to do all kinds of computations?
If it produces a correct response, the neural path/the tissue gets electrically stimulated.

Animal brain tissue can't do it well enough because it has a low number of layers.
Humans have 7 cortical layers unlike animals, which could make the tissue to wonderful computation if subject to the fast electrical training conditions of a laboratory.

It could be linked to a usual electric computational device, and complement regular computation.