TBy Anastasia Wasko
he practice of yoga nidra has the wonderful effect of calming the mind, but did you know that it also changes the activity in the brain? Yoga nidra (yoga sleep) is a thing you do as well as an object of devotion—both act as ways to put your mind and your brain into a state of relaxation. This enables the brain to experience the benefits of self-healing as well as heightened states of creative flow. 
The neurologic activity in an altered state of consciousness (such as yoga nidra) is measured by EEG. An EEG shows the brain’s activity as waves: delta waves are consistent with non-REM sleep; theta waves appear in altered states such as in meditation, hypnosis, dream, and “hypnogogic imagery.” Alpha indicate deep relaxation and beta are the waking state. Gamma waves indicate several motor processes and sensory stimulation processes are happening.
During a relaxing and meditative yoga nidra session, the brain’s alpha and theta waves become predominant, while deeper yoga nidra—the type experienced by the most advanced yogis—causes the brain to produce delta waves. The most advanced practitioner of yoga nidra might attain a state where the mind simultaneously remains “sleeping” and simultaneously “aware”—it is during this experience you become aware of the kundalini energy. In the highest form of meditation, somewhere between samadhi and nirvikalpa—no thinking and no thoughts—it is hypothesized that brain waves do not emit any measurable electrical activity.