Not sure what you mean by this. Quantum mechanical behavior happens all the time - everywhere (including in the brain). The question is whether quantum mechanical wave function interference effects affect thinking. I believe there are quite a lot of people who do not agree with the statement above.
The question isn't whether or not QM behavior is happening in the brain, it is whether or not meaningful coherent patterns in an information theoretic sense can be encoded in the QM substrate in an environment like the human brain. The argument is that even if QM effects are affecting the brain, it necessarily amounts to nothing more than noise due to environmental factors preventing any kind of persistent structure.
In a broader sense, the only thing we really know about the computational process of the human mind is that it is finite state machinery (this is something that can be measured and tested without knowing the mechanics of the machinery). This narrows the scope a lot, and even if there was QM machinery at work, then it must be a fairly simple finite state version of it. Note that this eliminates the necessity for QM behaviors as an explanation, as any FSM model that uses QM can necessarily be expressed as an ordinary boring FSM by definition. This is a much classier and more rigorous argument, but I don't bring it out much because it requires a little deeper understanding of the relevant points. In a nutshell, any QM behaviors that affect cognition must be FSM in nature based on measurable properties of the mind, which means that the human mind (in all its glory), must be expressable on any universal Turing machine (like ordinary silicon processors). Therefore, the QM argument is probably a moot point in any case, and at best would only affect the computational complexity of certain types of computations in implementation. It would not prevent the implementation of equivalent systems in ordinary silicon.