Biofeedback is a form of alternative medicine that involves measuring a subject's bodily processes such as blood pressure, heart rate, skin temperature, galvanic skin response (sweating), and muscle tension and conveying such information to him or her in real-time in order to raise his or her awareness and conscious control of the related physiological activities.
By providing access to physiological information about which the user is generally unaware, biofeedback allows users to gain control over physical processes previously considered automatic. Interest in biofeedback has waxed and waned since its inception in the 1960s; at the beginning of the 21st century it is undergoing something of a renaissance, which some ascribe to the general upswing of interest in alternative medicine modalities. Neurofeedback has become a popular treatment for ADHD; electromyogram (muscle tension) biofeedback has been widely studied and accepted as a treatment for incontinence disorders, and small home biofeedback machines are becoming available for a variety of uses. Its role in controlling hypertension is becoming recognised .
Types of biofeedback instrumentation
An Electromyogram is the most common form of biofeedback measurement. An EMG uses electrodes or other types of sensors to measure muscle tension. By the EMG alerting you to muscle tension, you can learn to recognize the feeling early on and try to control the tension right away. EMG is mainly used as a relaxation technique to help ease tension in those muscles involved in backaches, headaches, neck pain and grinding your teeth (bruxism). An EMG may be used to treat some illnesses in which the symptoms tend to worsen under stress, such as asthma and ulcers.
Peripheral skin temperature
Sensors attached to your fingers or feet measure your skin temperature. Because body temperature often drops when a person experiences stress, a low reading can prompt you to begin relaxation techniques. Temperature biofeedback can help treat certain circulatory disorders, such as Raynaud's disease, or reduce the frequency of migraines. The physiological process behind the temperature drop associated with the stress response is quite simply vasoconstriction (blood vessels narrowed by the smooth musculature in their walls)
Galvanic skin response training
With Galvanic skin response training, sensors measure the activity of your sweat glands and the amount of perspiration on your skin alerting you to anxiety. This information can be useful in treating emotional disorders such as phobias, anxiety and stuttering. This is the method most commonly used by lie detector machines. It is the most popular form of biofeedback, with over 500,000 hand-held GSR2 units having been purchased by consumers since the early '70s; it is also one of the biofeedback methods used by Calmlink and the video game series Journey to Wild Divine. Galvanic Skin Response meters are also now gaining popularity in hypnotherapy and psychotherapy practice where subtle physiological changes indicating emotional arousal can be more easily detected than by observation alone.
An EEG monitors the activity of brain waves linked to different mental states, such as wakefulness, relaxation, calmness, light sleep and deep sleep. This is the least common of the methods, mostly due to the cost and availability of an EEG machine.
Neal Miller, a psychology Ph.D and neuroscientist who worked and studied at Yale University, is generally considered to be the father of modern-day biofeedback. He came across the basic principles of biofeedback while doing animal experimentation conditioning the behavior of rats. His team found that, by stimulating the pleasure center of a rat's brain with electricity, it was possible to train them to control phenomena ranging from their heart rates to their brainwaves. Until that point, it was believed that bodily processes such as heart rate were under the control of the autonomic nervous system and not responsive to conscious effort.
The Miller group was one of three major approaches to understanding the limits of self-regulation of the body. Voluntary control of the autonomic nervous system had been considered impossible, only controlled by conditioning. Other threads of inquiry leading to "biofeedback" emerged from clinical attempts to use mind/body self-regulation techniques in healthcare. Elmer Green, PhD of the Menninger Foundation produced some of the original research on the limits of human self-regulation of normally unconscious processes and applied these techniques successfully to migraine headache and hypertension. Barbara Brown, PhD actually coined the word "biofeedback" during the early days of the field, as the Biofeedback Research Society was being formed. Other early pioneers were interested in "consciousness" and looked at EEG self-regulation as a way to approach mind vs. brain distinctions - see the work of Joe Kamiya, PhD. Other early efforts were directed toward examining the claims of yogis and other meditators for demonstrated mind/body control and markers of states of consciousness. See Elmer Green et al Beyond Biofeedback and Barbara Brown Stress & The Art of Biofeedback for some early writings. The Biofeedback Research Society evolved into the Biofeedback Society of America and more recently the Association for Applied Psychophysiology and Biofeedback, a scientific and professional society for the field.
An HEG is a method of functional infrared imaging that indirectly measures neural activity in the brain. There are two known types of HEG, passive infrared (pIR) and near infrared (nIR). Near Infrared HEG relies on the measurement of the differences in the color of light being reflected back through the scalp by the relative amount of oxygenated and unoxygenated blood in the the brain. Passive Infrared relies on the measurement of the heat being radiated from the scalp at locations of interest.
Biofeedback in art
Biofeedback data and biofeedback technology have been used by Massimiliano Peretti in a contemporary art environment, the Amigdalae project. This project explores how emotional reactions filter and distort human perception and observation. During the performance, biofeedback medical technology, such as encephalography, body temperature variations, heart frequency and galvanic responses, will be used to analyze people's emotional status as they watch video art. Using these signals, the music will change, so that the consequent sound environment will simultaneously mirror and distort the viewer's emotional state.  
More information is available at the website of the CNRS French National Center of Neural Research 
Biofeedback and Religion
Worldwide, exercises to develop biofeedback awareness have been used for centuries by various religious and spiritual orders (Yoga is one example.)
Not all of biofeedback's uses are well-accepted in the medical community. While biofeedback is widely accepted as a treatment for incontinence, other uses are still controversial. For instance, while many scientific studies have studied neurofeedback as a treatment for Attention Deficit/Hyperactivity Disorder     it is generally felt that neurofeedback is a "promising" rather than "proven" treatment modality . EEG biofeedback as a treatment for ADHD is viewed with skepticism in some parts. Additionally, some believe that the use of biofeedback for stress and anxiety is an expensive way to treat difficulties which could be addressed with relaxation training, meditation, and self-hypnosis.
Notes and references
- Harvard Gazette
- Biofeedback FAQ from the Mayo Clinic
- University of Vienna: Biomedical Engineering, Electromyography (EMG)
- Stress et biofeedback, bioamplificateur, EMG (French)
- Simple electronic apparatus of recording of EMG (Escuela de Ingeniera de Antioquia, Colombie)