This depends on the topic. If the conceptual framework of a topic is settled or understood, professionals are much more competent. For example if the question is “what is the neuroimaging data on the human reward system?” then a cognitive neuroscientist is the one to turn to for an answer.
If however the topic is an unanswered question, it can be anyone’s ball game. This is particularly true for topics that require less specialized knowledge. In this case amateurs can play a role.
For example, consider the question “what exactly is the mind (or consciousness) and how does it connect to the brain?” This is a very basic question at the heart of cognitive neuroscience. Can any cognitive neuroscientist answer this question? No. These folks do great work and know a lot about their subject matter. But they are no closer to answering this question – with clarity and precision — than Donald Hebb was 70 years ago.
Of course this question does require knowledge of the subject matter (in this case, mind and brain). But because the question is so broad, and of a philosophical nature, amateurs can have a say. And in this case one could argue knowledge is an impediment because of the associated philosophical assumptions. For example, a common assumption is the mind isn’t as important as the brain, and therefore the brain can be understood apart from the mind. This may or may not be true. But what IS certain is one needs to SET ASIDE this assumption in order to take a clear and objective look at the question.
The bottom line is there are certain topics in brain science that are accessible to not only professionals, but amateurs as well.