1. EEG rhythms change in concentration, wakefulness, REM, and dreamless sleep.
2. The states of consciousness- waking, dreaming, dreamless sleep- correspond to the realms of being- gross, subtle, causal.
3. Representation in the brain may be at least partly implemented by "binding rhythms", where a set of neurons (which may be distributed over a large physical space in the brain) become synchronized and thereby act as a functional unit.
So if delta sort of corresponds to the witness, maybe that's just the pure fact of representation (which is what creates subject/object), a slow rhythm involving many neurons that would in waking be separately representing various forms.