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1. What is biofeedback?
2. We can various types of biofeedback machines.
3. Our brain waves signify our state.

What is biofeedback? It is a technique by which a machine "feeds back" information about a physiological condition -- such as muscle tension -- so that we can try to change that condition. The feedback can be in the form of sounds or lights from the machine; for example, various sounds would indicate various levels of relaxation. Biofeedback is useful because:

1. It can detect states which might be too subtle for us to notice. For example, it would discern a slight increase in blood pressure.
2. It gives feedback on our attempts to change our state. For example, when we experiment with different relaxation techniques, the machine will tell us precisely how relaxed we have become (as indicated by a particular gauge, such as our brain waves). Biofeedback devices can measure our degree of stress, so it has been used to treat high blood pressure, migraine headaches, insomnia, and other disorders.

We can various types of biofeedback machines. A device might measure either our skin temperature, muscle impulses, heart rate, breath rate, GSR (galvanic skin response -- resistance to the body's electricity), or the type of brain waves (as described below). Each machine has different purposes; for example, a skin-temperature biofeedback device is frequently used in the treatment of hypertension.

Our brain waves signify our state. The four categories of brain waves are beta, alpha, theta, and delta, as measured in "cycles per second" (CPS).

1. Beta. (14 to 40 CPS). During our typical waking state, we are at approximately 20 CPS; we are busy, and our mind is actively processing data (and probably jumping from one subject to another). At a faster CPS rate, we are nervous, excited, or emotional, and we are unable to concentrate.
2. Alpha. (8 to 13 CPS). We are relaxed, dreamy, and creative. Many people use biofeedback to seek this "alpha state."
3. Theta. (4 to 7 CPS). This is the state of hypnosis, deep sleep, or profound meditation.
4. Delta. (1/2 to 3 CPS). We are in very deep sleep.