[uoaei]

It's an apples-to-oranges comparison. They're both fruit that grow on trees, but that's where the similarities end.

The primary difference, and likely the reason that brains are unreasonably effective, is the specifics of the architecture and internal representations (in the rigorous, information-theoretic sense) of its computational systems. It's not quite analog but it uses analog means. It's not quite digital but it does process via abstractions.

You can still reasonably call the brain a "computer" if you decide it can shed the laden history of that word and its close association with binary operations using transistors. You can do so because it uses internal structures to process inputs and emit outputs. But like I said above, it requires a generalized interpretation of the word to start to understand where and how the two fields of study may be unified.