What Are Alpha and Theta Brain Waves?

Brain waves are patterns of electrical activity produced by the coordinated activity of large populations of neurons. They are measured using electroencephalography, or EEG, and are commonly described according to their frequency. Alpha waves generally fall around 8–12 Hz, while theta waves generally fall around 4–8 Hz. These patterns are not simply “on” or “off”; the brain produces many frequencies at the same time, and their prominence changes depending on what we are doing, thinking, and experiencing.

Alpha activity is often associated with relaxed wakefulness, particularly when the eyes are closed and external sensory information is reduced. You might notice this kind of relaxed mental state when sitting quietly, resting, or allowing your attention to turn inward. Theta activity is commonly associated with drowsiness, certain stages of sleep, memory processes, and internally focused states. Both alpha and theta activity can occur naturally throughout everyday life, so neither brain wave is unique to hypnosis.

During hypnosis, researchers have observed changes in brain activity and connectivity, but it is too simplistic to say that hypnosis is simply an “alpha state” or a “theta state.” Hypnosis is a complex experience involving attention, expectation, perception, cognition, and brain-network communication. Rather than thinking of brain waves as a simple hypnosis switch, it is more accurate to think of them as one part of the brain's constantly changing electrical activity.

This distinction matters because popular descriptions sometimes suggest that entering theta automatically means entering hypnosis. It doesn't. The brain is always producing multiple rhythms, and the meaning of a particular rhythm depends on what the brain is doing at the time. In hypnotherapy, changes in brain activity occur within a much larger experience involving focused attention, reduced distraction, imagery, suggestion, and altered processing of internal and external information.