This is why you should never censor in brainstorming. If you censor the trigger, you never get the free associations. If you censor the free associations, you never get to make the connection between them and the question. Or in other words, if you censor, you never get to the solutions.
You can use this process of triggering and associating in many different forms of brainstorming.
Next time you feel blank, try brainstorming with these four steps:
1) Identify question
2) Pick a concrete trigger
3) Free associate
4) Build a bridge from the free association to a solution