Biofeedback is an umbrella term that means using the body to receive feedback, which the subject can then adjust in order to produce different feedback. Body systems used in biofeedback include heart rate, sweat production (Galvanic Skin Response), and EEG. EEG biofeedback is called neurofeedback.
GSR (Galvanic Skin Response) or EDR (Electro Dermal Response) measures the impedance of the skin. This impedance is mainly determined by the sweat gland activity in the intact skin. For GSR measurement preferably AG/AGCl electrodes are used with and isotonic electrode paste or gel. No skin preparation must be used other then maybe cleaning with alcohol. It takes a few minutes after electrode application before the signal becomes stable. Therefore when measuring GSR in combination with other measurements start with the electrodes for the GSR.
The analysis of heart rate variability (HRV), or heart rhythms, is a noninvasive means of measuring heart–brain and autonomic nervous system dynamics as influenced by one’s emotional state. Clinical research indicates HRV as a primary indicator of neurocardiac fitness and overall health. Abnormally low HRV is a predictor of premature mortality and is associated with a wide range of health problems, many of which can be stress-related. By influencing shifts in heart rhythms, one can positively lower stress levels, and thereby influence neural, hormonal and biochemical responses, yielding improvements in blood pressure, immune system function and so on. Effects may be both immediate and long-lasting.
By means of exercise the brain actually grows, very much like a muscle. If you exercise your brain in various ways, it will get larger. The brain needs connections between the various neurons in order to handle new information so the process can be one of increasing the blood supply and increasing the information (via blood supply).
Everything we learn to do, we do repetitively. So, we do Neurofeedback repetitively. Changes slowly develop, because each time we exercise our brain, we build. With HEG, this applies primarily to the development of new blood pathways. This is angiogenesis, developing the available blood supply. This process leads to dendritic growth—a bulking up of the brain. Herschel Toomin, inventor of the HEG, thought that using the HEG increased IQ by 10% within 20-40 sessions.