Try reading the post again. The question at issue is whether rationality always wins. If nothing you can do can make you, the rationalist, win, then rationality loses. That's part of the point.

Then it's a trivially obvious point. There's no need to talk about mind-reading deities and fMRI exams; any scenario where the rationalist doesn't get what he wants because of circumstances beyond his control would be an equivalent example:

• If a rationalist is fired because of the economic depression, then rationality 'loses'.

• If a rationalist's wife leaves him because she's discovered she's a lesbian, then rationality 'loses'.

• If a rationalist is hit by a meteor, then rationality 'loses'.

What makes your fMRI example seem different is that the thing that's beyond our control is having the kind of brain that leads to rational decision-making. This doesn't change the fact that we never had the opportunity to make a decision.