As a human being, a biological entity, conveying a thought or experience to another human being in a physical body, it seems that the brain must be involved. However, I cannot be certain that there is not something else at play. In my many out of the body experiences there has been communication, experiences, and expressions of ideas without a physical body or brain, or the physical senses. What exactly is taking place is not clear to me, though I have had more than a thousand such experiences. I am okay with saying that I just don't know. I have some ideas on this, but we can leave them for another discussion.
Maybe it's best if I said that to know or have a realization of the void does not necessarily involve the brain except in the act of remembering and attempting to explain what this is like to another physical person by way of language, writing, art, etc..
There are things that just cannot be adequately explained.
I would also state that the human experience may be limited to thought, but there is also experience that is not limited to thought, and for a lack of a better word we may call such an experience mystical or spiritual, although the connotation of these words has created much confusion and misunderstanding.
I am curious about your use of the word hallucination. The definition refers to a sensory perception (such as a visual image or a sound) that occurs in the absence of an actual external stimulus and usually arises from neurological disturbance (such as that associated with delirium tremens, schizophrenia, Parkinson's disease, or narcolepsy) or in response to drugs (such as LSD or phencyclidine). So I think the word hallucination is inaccurate when it comes to the mystical experience and seems quite derisive and dismissive.
I also feel as though the idea that the mystic learns how to dissolve the personal self is a bit simplistic and misleading. It is not the dissolution of the self that occurs (at least partially because the self doesn't exist except as an idea combined with a state of attention), but rather seeing the self for what it is and finding/seeing/experiencing what lies prior to the self. The void is ever-present, which is why I previously said that to know it is more a matter of elimination than acquisition or the attainment of a certain state. It's more like the void is always present yet due to our identification with the body and all its associations/identifications, our attention upon the matters of the body disallow us from realizing ourselves as the void.
By way of a crude analogy, a man named Dave who is a father of two and husband can hop on his bike and ride to a nearby hospital, enter the building and don a white coat and be presented to the world as Dr. David Goldberg, surgeon extraordinaire. Now at work, Dave's attention is on his role as a physician. He was a physician at home, and he's still a father and husband at work. When he goes out to dinner with his wife he is still a surgeon, and he is still a surgeon when he himself becomes a patient to remove a mole from his elbow. What has changed? Dave is also the void as well as consciousness, or life energy or whatever we want to call it.
To know that you are the void (I think capacity may be a better word) is a knowing that does not involve thought except when that knowing is conveyed to someone else.
As a caveat I would add that, of course, there are people who are just conning other people and saying that they are enlightened, etc. But for the sake of our conversation here I'd rather focus on that which is sincere. And I would reiterate that the biggest problem with all of this is that the effort to understand that which does not arise out of thought is futile. Further, speaking to your question, the brain does not need to remember being the void or "in that state." The knowing is clear and ever-present in the same way that you do not need to remember that you are alive.
