A variable psychophysiological function that can be approached by the biofeedback method is electric skin activity.
The feedback signal is based upon changes monitored in the electric activity of the skin.
Electrodermograph or simply dermograph or G.S.R from the initials of Galvanic Skin Resistance, is the device recording skin electric activity and has been used in an assortment of clinical and laboratory applications.
A laboratory dermograph is a small portable instrument with 3 volt battery supply which is connected through optical fibers to the computer. Its electrodes are always placed on fingers or palms. Changes in skin electric activity are recorded either as resistance (OHMS) or conductance changes (MHOS) and transformed into visual or acoustic signals fed back, in succession, to the trainee.
The electric activity skin presents is chiefly accountable to changes occurring in its electric resistance.
The electric activity of the skin depends on the activity of the perspiration glands: the greater the activity of the latter the more perspiration is excreted and the lower the skin’s electric resistance. Sweat is a good conduit for the electric current, therefore the more we sweat the more current passing increases, and consequently resistance decreases. Perspiration glands stretch all over the body and are divided in holocrine and apocrine. However at palms and soles prevail the apocrine type. In axillae and genital organs area are located the holocrine glands.
So at the fingers or palms, the areas used in biofeedback, are found apocrine glands.
Diminutive changes in the activity of perspiration glands, meaning quantitative changes in secretions, bring about respective changes in electric skin resistance. However, the perspiration glands operation is controlled by the autonomic nervous system in such a way that greater sympathetic arousal, namely stress, leads to greater gland activity, therefore greater amounts of sweat, and consequentially lower skin resistance.
Another factor affecting electric skin activity is the circulation of free ion systems under the epidermis. The circulation of these ions depends on the blood flow inside the arterioles and venules of the skin, the diameter of which and the resultant blood supply is controlled by the autonomic nervous system. The correlation is of the type that increased sympathetic activity, occurring when you are stressed, induces vasoconstriction, ions supply reduction and thus reduction of the monitored skin resistance. The electrodermograph detects and measures autonomic nervous arousal through two channels. Firstly, through skin perspiration secretion, which causes fluctuations in skin electric resistance, and secondly through free ions circulation which varies according to the peripheral vessel constriction or dilation.
This makes obvious that electrodermal activity reflects the general arousal or “discharge” of the autonomic nervous system with respect to to the functioning of your psychoemotional organ.
The dermograph provides you with information upon the level of the psychoemotional stress you experience.
Τhere are various ways of measuring electrodermal activity. The most common is by measuring skin electric resistance or, as is usually refered, galvaning skin resistance. The galvanic skin resistance decreases when the activity of perspiration glands increases and when ions circulation under epidermis decreases.
Another method, less common, used to estimate electrodermal activity is by measuring skin voltage emerging from the circulation of the above mentioned free ions.
If we observe the ranging of electrodermal activity, we will notice two phenomena: the tonus level or else baseline and the interim respones or phase responses. The baseline of electrodermal activity resemles the muscular tonus: it is a constant activity, in this case of electrodermal nature, which shows only very slow changes. The baseline usually is refered as the skin conductance baseline or as the skin voltage baseline.
A phase response indicates a change in electric skin activity as response to some internal or external stimulus. Phase response variations are considerably more rapid and bigger than those observed at baseline. The time required for the completion of the reaction, the inertia or inaction period, the level it will reach, the response peak, the time it stays at this level, the preservation time and the time needed in order to return to the pre-stimulus electrodermal activity are parameters supplying the trainee in electrodermal biofeedback with very important information.
The dermograph is the instrument that supplys you with information on your psychoemotional condition. It records the psychoemotional responses occurring inside the organism under the influence of certain stimuli.
You realize and classify the influences and stimuli you receive, however you are ignorant of the psychoemotional impact they breed upon your organism. Besides any superficial, perceived impact, these factors deeply and essentially influence effect your psychomental homeostasis and body functions.This dermograph detects and reveals this profound impact. Studies have been carried out on high blood pressure patients, on patients with phobias, panic attacks, on women during labor, on athletes dealing with pre-game or game stress etc.
The electrodermograph measures certain functions of the autonomic nervous system, and shows you the degree of arousal or relaxation in your body. Learning with the help of this device how your organism works will make you realize how much you can affect your health and physical condition.
This way you learn about the link connecting your psychomental or somatic dysfunctions and the feelings you daily experience. Finally, you get the chance to desensitize from the influences disordering your inner functions and homeostasis. Without the electrodermograph biofeedback resembles a top school deprived of its professors.
And of course all these instinctively, under the need to survive.
Electromyograph is the proper device for measuring, recording and informing you about the load of tension on your muscle groups. It provides you with feedback and objectively informs you every time you succeed or fail to relax or desensitize you muscular system. You know from an objective source what you must incorporate and what needs to be re-examined and corrected. Without the electromyograph your attempts to know and relieve your muscular system resembles trying to fly an airplane without wings.