In biofeedback ultra-modern sophisticated instruments are used to measure physiological responses. by this technique a person learns how to regulate certain body functions, such as heart rate, blood pressure, or brain wave patterns, that are normally considered to be involuntary. So we may say, biofeedback is a method for learning to increase one's ability to control biological responses, such as blood pressure, muscle tension, and heart rate. The name biofeedback refers to the biological signals that are fed back, or returned, to the patient in order for the patient to develop techniques of manipulating them.

Biofeedback enables a person to gain some element of voluntary control over autonomic body functions.
It may be used clinically to treat certain conditions, such as hypertension and migraine headache.
Biofeedback may also be useful for the following health problems:
• anorexia nervosa
• anxiety
• asthma
• autism
• back pain
• bed wetting
• chronic pain
• constipation
• depression
• diabetes
• fecal incontinence
• epilepsy and related seizure disorders
• head injuries
• high blood pressure
• learning disabilities
• motion sickness
• muscle spasms
• sexual disorders, including pain with intercourse
• spinal cord injuries
Biofeedback has been used to successfully treat a number of disorders and their symptoms, including temporomandibular joint disorder (TMJ), chronic pain, irritable bowel syndrome (IBS), Raynaud's syndrome, epilepsy, attention-deficit hyperactivity disorder (ADHD), migraine headaches, anxiety, depression, traumatic brain injury, and sleep disorders.
Illnesses that may be triggered at least in part by stress are also targeted by biofeedback therapy. Certain types of headaches, high blood pressure, bruxism (teeth grinding), post-traumatic stress disorder, eating disorders, substance abuse, and some anxiety disorders may be treated successfully by teaching patients the ability to relax and release both muscle and mental tension. Biofeedback is often just one part of a comprehensive treatment program for some of these disorders.
NASA has used biofeedback techniques to treat astronauts who suffer from severe space sickness, during which the autonomic nervous system is disrupted. Scientists at the University of Tennessee have adapted these techniques to treat individuals suffering from severe nausea and vomiting that is also rooted in autonomic nervous system dysfunction.

Side Effects of Biofeedback
There are no known side effects to properly administered biofeedback or neurofeedback sessions.
 

Training & Certification in Biofeedback
Individuals wishing to try biofeedback should contact a healthcare professional trained in biofeedback techniques. Licensed psychologists, psychiatrists, and physicians frequently train their patients in biofeedback techniques, or can recommend a specialist who does. In some cases, a licensed professional may employ a biofeedback technician who works under their direct guidance when treating patients. There are several national organizations for biofeedback therapists, including the Biofeedback Certification Institute of America, which also certifies therapists in the practice.


Types of biofeedback instrumentation
Electromyogram (EMG)
An electromyogram (EMG) is a test that is used to record the electrical activity of muscles. When muscles are active, they produce an electrical current. This current is usually proportional to the level of the muscle activity. An EMG is also referred to as a myogram. EMGs can be used to detect abnormal muscle electrical activity that can occur in many diseases and conditions, including muscular dystrophy, inflammation of muscles, pinched nerves, peripheral nerve damage (damage to nerves in the arms and legs), amyotrophic lateral sclerosis (ALS) (also known as Lou Gehrig disease), myasthenia gravis, disc herniation, and others.
An Electromyogram is the most common form of biofeedback measurement.

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.
 

Electroencephalography (EEG)
Brain waves are attributed to electrical activities of the brain which are manifest as alternating potential differences at the scalp surface. When acquired through scalp electrodes, such potential differences result in time-continuous signals termed electroencephalogram (EEG). From a physical point of view, it is opportune to model the wave-like qualities of EEG as a finite sum of harmonic oscillations at discrete vibration rates triggered by a central pace-maker. Hence, brain-waves can analoguously be interpreted like sound waves in acoustics which consist of a fundamental oscillation superimposed by higher harmonics. Each of these partial tones is uniquely characterized by 2 quantities, its frequency ("pitch") and its amplitude ("loudness").
An EEG monitors the activity of brain waves linked to different mental states, such as wakefulness, relaxation, calmness, light sleep and deep sleep.