There is extensive research into the anatomy and functions of the brain. Studies into the the frequencies of brainwaves have led to the classification of various
conscious states. Here is a little technical stuff to summarize what happens inside the brain during altered states of consciousness.
Normal waking consciousness:
Low amplitude beta wave, or beta rhythms above 12 Hertz (12 transitions or cycles per second) includes multiple and varying frequencies when we are awake.
Higher Mental Activity, Perception and Consciousness:
Gamma waves, 40 Hertz (Hz), can often be between 26 and upwards of 70 Hz. Gamma waves are involved in higher mental activity, such as when there are periods of
synchronized firings of entire banks of neurons from different parts of the brain. This activity has been proposed as a mechanism for perception and recognition of
new insights. Higher level cognitive activities occur when lower frequency gamma waves suddenly double into the 40 Hz range and higher. Research has shown gamma waves
are continuously present during low voltage fast neocortical activity (LVFA), which occurs during the process of awakening and during active rapid eye movement (REM)
Alpha waves, 12.39 ~ 8.2 Hz, are commonly detected by electroencephalography (EEG) or magnetoencephalography (MEG) and originate from the occipital lobe during periods
of relaxation, with eyes closed but still awake and during drowsiness. They are thought to represent the activity of the visual cortex in an idle state. This state
includes inspiration, mental channelling, mediums and clairvoyance. etc.
Theta waves, 8.19 ~ 4.3 Hz, includes light trance, partial loss of awareness to deeper trance associated with various sleep and wakefulness states. Theta rhythms are
observed in awake children under the age of 13 years, in some in adults during rapid eye movement (REM) sleep and in states of quiet focus, for example deeper
meditation. These rhythms are associated with spacial navigation and some forms of memory and learning, especially in the temporal lobes. Electrophysiological or
pharmacological stimulation also can induce trances.
Delta waves, 4.29 ~0.59 Hz, occur when the body is completely passive characterized by deep sleep, very deep trance, feelings of being out of the body and control by
spirit guides and coma. It is normal in awake children under the age of 13.
0.49 ~ 0.01 Hz Where Have You Gone?