http://www.neuronic.com/alternat_files/meditation_and_sleep.htm

http://www.sawka.com/spiritwatch/fromlucid.htm
here's an excerpt from the paper at this site:
              Physiological Analysis of the Lucidity–Witnessing Relationship
I shall first consider the relationship of meditation to REM sleep on a physio-logical level of analysis. Meirsman (1989) studied six advanced TM meditators (TM-Sidhi techniques) who reported witnessing sleep on the average of half the night. He argued that the practice of the TM-Sidhis results in the "maintenance of . . . alertness even during the inertia of deep night sleep" and that further "‘witnessing’ of one’s own sleep during the night seems to be the subjective experience of a physiologically more efficient (REM) sleep." Meirsman examined the incidence of an eye movement ratio (high frequency REMs/low
frequency REMs [HF/LF]) from uninterrupted REM sleep (no prearranged eye movement signals were required). HF/LF had been shown to be "associated with cerebral maturation (age, second half of ovulatory cycle, second half of pregnancy)." Meirsman points out that this measure can be "defined as the capacity of the brain to structure ‘order’ from the ‘noisy stream’ of information." This researcher found that the REM sleep of the meditators who were conscious during it was more order-creating (higher HF/LF ratios) than that of the "unconscious" nonmeditators. He describes this as "a reflection of the higher
inten-sity of the assimilation of information in the brain during REM sleep." This finding was further supported by the shorter REM sleep time among the meditators in his study when compared to his controls.

Unfortunately, meditation practice in this study is confounded with reports of witnessing. According to the teachings of this meditation practice, a result of the practice will be sleep consciousness. Although spontaneous occurrences at this fre-quency (half the night or more) may occur, they are so rare as to be virtually non-existent, whereas Gackenbach, Cranson and Alexander (1987; 1989) have shown that such high rates are not infrequent in groups of TM meditators. Thus it may be nearly impossible to separate sleep consciousness at this rate from the practice of meditation.

I will now fold the Meirsman study back onto the physiological analysis of lucid dreaming reviewed earlier. The most reliable physiological finding in the lucid dreaming literature is the association of high REM density to the lucid state in REM. Likewise, Meirsman reported that the total REM density regardless of frequency, was also significantly higher for the TM-Sidhi group when compared to controls. LaBerge (personal communication, March, 1989) compared the REM density of twelve lucid dreamers to that of Meirsman’s six meditators. Although the means were the same, variability among the lucid dreamers was quite high whereas it was virtually nonexistent among the meditators. In other words, both lucidity and witnessing (as a product of meditation) evidence the same increase in REM density, but the meditators were more stable, on the physiological level of analysis, in their experience.

http://web.us-com/contents2htm

    Monks, Shamans, Drum Beats, Primitive Cultures, Rhythmic Sound & The Brain
Studies have shown that vibrations from rhythmic sounds have a profound effect on brain activity. In shamanic traditions, drums were used in periodic rhythm to transport the shaman into other realms of reality. The vibrations from this constant rhythm affected the brain in a very specific manner, allowing the shaman to achieve an altered state of mind and journey out of his or her body .
 Brain pattern studies conducted by researcher Melinda Maxfield into the (SSC) Shamanic State of Consciousness found that the steady rhythmic beat of the drum struck four and one half times per second was the key to transporting a shaman into the deepest part of his shamanic state of consciousness. It is no coincidence that 4.5 beats, or cycles per second corresponds to the trance like state of theta brain wave activity. In direct correlation, we see similar effects
brought on by the constant and rhythmic drone of Tibetan Buddhist chants, which transport the monks and even other listeners into realms of blissful meditation.
The gentle pulsating rhythms (binaural beat) of our brain synchronization tapes act in a similar fashion, yet because the frequencies are computer generated, they are precise, consistent and can be targeted to induce highly specific and desired brain states. Much like tuning a radio to get a particular station, our brain synchronization tapes can induce a variety of brain states. Effecting Alertness, Concentration, Focus & Cognition Relaxation, Visualization, &
Creativity Intuition, Memory, Meditation Vivid Visual Imagery Deep Sleep, Detached Awareness
There are frequencies/rhythms which when dominant in the brain correlate with a specific state of mind. There are generally 4 groupings of brain waves:

1. Beta waves range between 13-40 HZ. The beta state is associated with peak concentration, heightened alertness and visual acuity. Nobel Prize Winner, Sir Francis Crick and other scientists believe that the 40HZ beta frequency used on many Brain Sync tapes may be key to the act of cognition.

2. Alpha waves range between 7-12 HZ. This is a place of deep relaxation, but not quite meditation. In Alpha, we begin to access the wealth of creativity that lies just below our conscious awareness - it is the gateway, the entry point that leads into deeper states of consciousness. Alpha is also the home of the window frequency known as the Schuman Resonance, which is the resonant frequency of the earth's electromagnetic field.

3. Theta waves range between 4-7 HZ. Theta is one of the more elusive and extraordinary realms we can explore. It is also known as the twilight state which we normally only experience fleetingly as we rise up out of the depths of delta upon waking, or drifting off to sleep. In theta we are in a waking dream, vivid imagery flashes before the mind's eye and we are receptive to information beyond our normal conscious awareness. During the Theta state
many find they are capable of comprehending advanced concepts and relationships that become incomprehensible when returning to Alpha or Beta states. Theta has also been identified as the gateway to learning and memory. Theta meditation increases creativity, enhances learning, reduces stress and awakens intuition and other extrasensory perception skills. When the brain is in Theta it appears to balance sodium/potassium ratios which are responsible for the transport of chemicals through brain cell membranes. This appears to play a role in rejuvenating the fatigued brain.

4. Delta waves range between 0-4 HZ. Delta is associated with deep sleep. In addition, certain frequencies in the delta range trigger the release of Growth Hormone beneficial for healing and regeneration. This is why sleep, deep restorative sleep is so essential to the healing process.

By the way, the above is more detailed than the material covered in your text.