It's a model for explaining improvements in cognitive function. The idea is that the brain's energy consumption is fixed, so when you improve its function on so

It's a model for explaining improvements in cognitive function. The idea is that the brain's energy consumption is fixed, so when you improve its function on something it costs you from elsewhere. So if you take Adderall to get better at school, you're not getting a brain improvement, you're just reallocating resources. It's more like moving money from your Chase account to your Wells Fargo account than it is like getting richer. During the lead up there are also interesting bits like "if you suppress one part of the brain another does better at its task" and models that explain the interesting behaviour.