"nothing really tastes [etc], it's just your brain's interpretation"

1 that brain is you

2 the interpretation constitutes the fact that it tastes or whatever, what else could that even mean?

If that's where that person ends up after "thinking too much"..

"A little learning is a dang'rous thing; Drink deep, or taste not the Pierian spring: There shallow draughts intoxicate the brain, And drinking largely sobers us again."