>What, exactly, is a brain wave?
Some stages of akasha moving?
>What does it measure, or reflect?
That depends on the sector.
>Is it really a wave form
The only time I perceived some (magic ones to do with someone else) in
my brain, they had regular wave shape,
but only as long as the other was constant on a "setting", when he
fuzzed to another one there were loads of energies that I did not
track. Don't recall much about them, but to me those did not seem like
regular wave shapes.
Might depend on the area and what you do.
Concerning tuning to other energies:
As such some areas can be tuned to overlay with external energies,
especially some of the energy sensor areas meant for such,
but with artificial ranges it might be questionable if it is healthy
to do that.
If wishing to tune to sleeping ranges, or other stages, it might be
healthier to have a consenting brain able to tune there and tune to
it. That is more natural than using artificial devices.