Biofeedback

Biofeedback is the process of becoming aware of various physiological functions using instruments that provide information on the activity of those same systems, with a goal of being able to manipulate them at will. Processes that can be controlled include brainwaves, muscle tone, skin conductance, heartrate and pain perception.

For this procedure, technological devices are used to measure varying bodily functions and presenting them to the user in real time. This is done for physiological procedures under the voluntary control of the nervous system, but not directly perceptible. Under servosystems jargon, this information is called "feedback", and when feedback is referred to biological functions, it's called "biofeedback".

Biofeedback is not a therapeutic procedure, but rather a training for the improvement or control over bodily capabilities of the human body. Learning to distinguish those capabilities and control them is no diffrent than learning how to play piano or tenis. Through that training we learn how to recognize our own unique psychophysiological patterns, while at the same time we learn how to gain control over them despite them having control over us.

Many physiological functions can be measured by biofeedback devices. The most common are:

1. Electromyography(EMG): An electromyograph uses surface electrodes to detect muscle action potentials (mictovolts) from skeletal muscles that initiate muscle contraction. Clinicians record the surface electromyogram (SEMG) using one or more active electrodes that are placed over a target muscle and a reference electrode that is placed within six inches of either active. The SEMG is measured in 
2. Thermometer: A feedback thermometer detects skin temperature with a thermistor that is usually attached to a finger or toe and measured in degrees Celsius or Fahrenheit. Skin temperature mainly reflects arteriole (small diameter blood vessels) diameter. Hand-warming and hand-cooling are produced by separate mechanisms, and their regulation involves different skills.
3. Electrodermography(EDG): An electrodermograph measures skin electrical activity directly (skin conductance and skin potential) and indirectly (skin resistance) using electrodes placed over the digits or hand and wrist. Orienting responses to unexpected stimuli, arousal and worry, and cognitive activity can increase eccrine sweat gland activity, increasing the conductivity of the skin for electrical current.
4. Electroencephalography(EEG): My favourite, an electroencephalograph measures the electrical activation of the brain from scalp sites located over the human cortex. The EEG shows the amplitude of electrical activity at each cortical site, the amplitude and relative power of various wave forms at each site, and the degree to which each cortical site fires in conjunction with other cortical sites (coherence and symmetry).
5. Photoplethysmiography(PPG): A photoplethysmograph measures the relative blood flow through a digit using a photoplethysmographic sensor attached by a Velcro band to the fingers or to the temple to monitor the temporal artery. An infrared light source is transmitted through or reflected off the tissue, detected by a phototransistor, and quantified in arbitrary units. Less light is absorbed when blood flow is greater, increasing the intensity of light reaching the sensor
6. Electrocardiography(ECG): The electrocardiograph uses electrodes placed on the torso, wrists, or legs, to measure the electrical activity of the heart and measures the interbeat interval (distances between successive R-wave peaks in the QRS complex). The interbeat interval, divided into 60 seconds, determines the heart rate at that moment. The statistical variability of that interbeat interval is what we call heart rate variability. The ECG method is more accurate than the PPG method in measuring heart rate variability.
7. Pneumography: A pneumograph or respiratory strain gauge uses a flexible sensor band that is placed around the chest, abdomen, or both. The strain gauge method can provide feedback about the relative expansion/contraction of the chest and abdomen, and can measure respiration rate (the number of breaths per minute).Clinicians can use a pneumograph to detect and correct dysfunctional breathing patterns and behaviors.
8. Capnometry: A capnometer or capnograph uses an infrared detector to measure end-tidal CO₂ (the partial pressure of carbon dioxide in expired air at the end of expiration) exhaled through the nostril into a latex tube. The average value of end-tidal CO₂ for a resting adult is 5% (36 Torr or 4.8 kPa). A capnometer is a sensitive index of the quality of patient breathing. Shallow, rapid, and effortful breathing lowers CO₂, while deep, slow, effortless breathing increases it
9. Rheoencephalography (REG), or brain blood flow biofeedback, is a biofeedback technique of a conscious control of blood flow. An electronic device called a rheoencephalograph is utilized in brain blood flow biofeedback. Electrodes are attached to the skin at certain points on the head and permit the device to measure continuously the electrical conductivity of the tissues of structures located between the electrodes. The brain blood flow technique is based on non-invasive method of measuring bio-impedance. Changes in bio-impedance are generated by blood volume and blood flow and registered by a rheographic device. The pulsative bio-impedance changes directly reflect the total blood flow of the deep structures of brain due to high frequency impedance measurements