Every few weeks there is a headline saying AI is rotting our brains, and a reply saying it is just a calculator for words. Both are wrong in the same way: they treat "using AI" as one thing. The research I went through points to something much more useful. The same tool can make you weaker or stronger, depending on one thing: whether the AI is doing the part of the work that was supposed to make you better. So instead of arguing, here is a way to sort every task you give an AI into three categories, with the evidence for each, and something you can copy.

Category 1: the effort IS the point. Do these with no AI involved. There was a small experiment done by MIT Media Lab's called "Your Brain on ChatGPT" (Kosmyna and colleagues, 2025). Fifty-four people wrote essays, either with an LLM, with a search engine or with only their own head, while EEG measured their brain activity.…