Duel
To dream that you are in a duel signifies internal disagreements or inner conflicts in which you need to find a middle ground. You need to stop seeing things in black and white.
Survey
To dream that you are taking a survey suggests that you are trying to assess your abilities and evaluate a situation. You need to determine if you have what it takes to achieve your goals. You are being put through some sort of test. Consider the type of questions being asked in the survey and how it applies to your waking life.
Brain
To dream of your brain suggests that you are under severe intellectual stress. You need to put your problem-solving abilities to use. Alternatively, it implies that your ideas are not receiving enough attention and validation. You are concerned that your knowledge and teachings are not be transmitted clearly.