The social engagement system has a control component in the cortex (i.e., upper motor neurons) that regulates brainstem nuclei (i.e., lower motor neurons) to control eyelid opening (e.g., looking), facial muscles (e.g., emotional expresssion), middle ear muscles (e.g., extracting human voice from background noise), muscle of mastication (e.g., ingestion), laryngeal and pharyngeal muscles (e.g., prosody) and head tilting and turning muscles (e.g., social gesture and orientation). (Porges, 2003b, p. 35)

Many of the early questions raised about the action of hallucinogens seem to have been answered. Hallucinogens, working through 5-HT2 receptors, lead to increased excitation in the brain, especially in the frontal and temporal cortex. Although this is an explanation of the cellular events produced by hallucinogens, it does not come close to explaining the plethora of subjective effects that are the hallmark of hallucinogen intoxication. Some researchers put forward the hypothesis that hallucinogens produce their effect by limiting the filtering effect of the thalamus (so-called sensorimotor gating) and hence allow a flood of sensory information to overwhelm the cortex. Although this explanation sounds intuitive, not only do the dissociative anaesthetics (PCP, ketamine) produce the same deficient gating of sensory information but so do methamphetamine and even schizophrenia (Vollenweider and Geyer 2001). Granted, there are some similarities between the effects of these drugs and some symptoms of mental illness, but anyone who has taken mescaline and LSD knows there is a similarity between these two classes of drug that is not shared with ketamine or methamphetamine. Ultimately, only when science fully understands how the brain is capable of producing cognition will we be able to understand how not only the phenethylamine and indole hallucinogens, but also how other psychoactive drugs affect the mind.
The Neuropharmacology of Hallucinogens - a brief introduction. v1 Feb 2004 (first draft June 2003) edited & published by Erowid [http://www.erowid.org/ ]

Drumming induces natural altered states of consciousness.

Chronic pain has a progressively draining effect on the quality of life. Researchers suggest that drumming serves as a distraction from pain and grief. Moreover, drumming promotes the production of endorphins and endogenous opiates, the bodies own morphine-like painkillers, and can thereby help in the control of pain.

Rhythmic drumming induces altered states, which have a wide range of therapeutic applications. A recent study by Barry Quinn, Ph.D. demonstrates that even a brief drumming session can double alpha brain wave activity, dramatically reducing stress. The brain changes from Beta waves (focused concentration and activity) to Alpha waves (calm and relaxed), producing feelings of euphoria and well-being.

Shamanic drumming directly supports the introduction of spiritual factors found significant in the healing process. Drumming and Shamanic activities produce a sense of connectedness and community, integrating body, mind and spirit. According to a recent study, “Shamanic activities bring people efficiently and directly into immediate encounters with spiritual forces, focusing the client on the whole body and integrating healing at physical and spiritual levels. This process allows them to connect with the power of the universe, to externalize their own knowledge, and to internalize their answers; it also enhances their sense of empowerment and responsibility. These experiences are healing, bringing the restorative powers of nature to clinical settings.
[Federation of Drums and Percussion LLC - Barberton OH]

When we drum and enter into ceremonial space, or what Harner calls the Shamanic State of Consciousness (what I call opening the dreaming eye, what Ken Wilbur calls opening the eye of Spirit) we step into this other universe where the life force interpenetrates everything, where the distinction between one sound and another begins to blur, and where small “I” and immense “Thou” begin to merge. The healing that shamans and energy healers do comes from their ability to step into that flow and then learn how to absorb Life Force and channel it. That channeling of the life force can take so many forms, and really one of your main tasks is to become open to the signals of what form it wants to take in you.

Because this Life Force is far too immense for us to comprehend (no less contact directly), we find ways to grasp it (or as the poet Rilke says “we are grasped by what we cannot grasp” – god, how I love that line!). We use metaphor and symbol to describe it and explain it to each other, and anyone truly aligned with Spirit understands that, as the 14th Century Meister Eckhart says, “All language has taken a vow to be wrong about God.” So we grasp at it with words that seem large to us, but are only small human words. In the shamanic path, we also comprehend the Life Force through personal imagery, through visions, dreams (night dreams, or half-awake drumming dreams). We contact the Life Force through power animals and spirit guides. These images are condensed parcels of Life Force that we communicate with, merge with, and allow to work through us. And we channel Life Force through learning spirit songs or dances, ceremonies, healing acts large and small, and through choosing certain ways to live and respond to this world. This is why we drum and why we journey to the spirit world – to step into this other, valid universe where the rules of how the life force works are different from the universe we live in most of the time.
http://www.drummingthesoulawake.blogspot.com/