I can share my experience from participating in three separate brainwave studies conducted on long-time meditators.
We were each hooked up to about 80 electrodes which recorded brainwaves, breathing, heart rate, oxygen level and a couple other things (I don’t recall). All this was done at a hospital facility and conducted by a senior sleep research doctor, who himself had practiced meditation for many years.
I don’t know the details of all the participants but in my case I was able to enter alpha level almost immediately - this is simply a state of deep relaxation.
One of the things they hoped to determine was, can a meditator reach delta sleep - deep sleep state and still be conscious? The study showed this was indeed possible.
Now, there are more studies coming along using neuroimaging (MRI) to see specific areas of brain activity in real time (if anyone out there is a researcher doing this type of research, I would like to participate!). I have not read all of this research but you can find it online. They have measured variations in brain connectivity and also enlargement of certain areas and shrinkage of certain areas of the brain (again please look up online).
So, this is my take on it so far - I have meditated over 40,000 hours over about 50 years. That is a lot of meditation! I have had many experiences that I would call awakening experiences. Some of these lasted a few days or a week and others were instantaneous and permanent shifts of consciousness.
It’s my feeling that, while there will likely be long term shifts in brain mass, which science has already documented, current technology that only looks at brain activity may not necessarily show any difference in a person who has had an awakening experience.
The reason is, we mistakenly believe that thought activity or lack of it has something to do with higher states of consciousness. This is not always true. It is natural for the mind to have activity and the attainment of higher spiritual states does not in anyway mean the annihilation of thought or thought activity.
It is more accurate to say that you transcend the effects of thought activity but you then use the mind instead of the mind using you.
This too, is only one stage. The master Babuji says, we ultimately transcend even consciousness. These states are not describable because our current conditioned state of perception doesn’t operate at that level. So, just as deep sleep state is not perceptible, superconscious states are also not perceptible or interpretable. We say we don’t remember them. Do you remember deep sleep? No. Do you remember deep meditation? It is possible with practice but most often, no.
I believe we do not currently have the technology to understand states that transcend brain activity itself. In other words, there may be levels of consciousness that are not reflected as brain activity.
The other point is, at the beginning of these type of experiments a baseline is taken from your current wakeful state in order to establish a reference point by which researchers can see deviations.
A person already permanently abiding in an awakened state is there all the time, regardless of all other states of wakefulness, or sleep states such as delta, theta and alpha, which are innate to the body and mind perception but not to subtle consciousness.
Imagine, we are here on the ground in the midst of a big city. We can only see what is around us - the hustle and bustle. We use all our body senses to interpret and navigate the surroundings of our body.
If we were somehow able to move our perception high in the sky, everything would be different - our awareness is now in a different atmosphere. We can see all around, its quiet, we see everything down below but we are no longer “in it.”
Imagine going further with awareness - to space. Now things again are very different - it’s a different atmosphere, now there isn’t even air pressure or gravity. The world is just a small ball in space.
These are examples to illustrate how consciousness can be aware in subtler and subtler inner atmospheres but yet the body is still here functioning as normal. How can we measure those subtle atmospheres when they are more subtle than measurable body functions?
So, these are a few thoughts, again from my own experience and not based on scientific study though I could argue that observing these things is also very much scientific study - but where instruments can’t yet go!
good studies.