Some yogis have extended their range of control over inner, normally involuntary processes in dramatic ways. Some can cause their heart rate to increase to five times its resting rate. Some are able to cause a ten-degree temperature difference between the thumb and little finger of the same hand: one side is flushed and hot, the other side cool and pale. Many other forms of self-control have been documented,[6] but acquiring these special skills through the practice of yoga takes years of discipline, concentration, and tenacity. But the years of dedication seem also to be indispensable if one is to develop the qualities of inner tranquility and strength sought by yogis. [6] See, e.g., Mircea Eliade, _Yoga: Immortality and Freedom_ (Princeton, NJ: Princeton University Press, 1958). Biofeedback has greatly shortened the yogis' road to conscious control of some physical processes, and, in turn, it has become the main contribution technology has made so far to psychotherapy. Many of the physical processes that biofeedback training can help you learn rather quickly to control influence your emotional well-being. Biofeedback equipment can enable you to learn, for example, how to _will_ a state of muscular relaxation, how to gain a measure of control over your physical response to stress or pain, even how to raise or lower your blood pressure or heart or respiration rate. To use biofeedback equipment, electrodes are taped to the areas of your body that are to be monitored. They may measure such things as skin temperature, skin moisture, muscle tension, pulse and breathing rates, or brain wave patterns. The feedback from which you learn to control normally involuntary processes occurs when the measurements made by the instruments are externalized for you: you are able to _see_ a pattern on a computer {213} monitor or oscilloscope or _hear_ a changing tone that gives you immediate information about your physical responses. In other words, biofeedback is an electronic way of representing inner processes externally that are usually automatic, involuntary, and unconscious. PHYSICAL APPLICATIONS Frequently, and relatively quickly, many people are able to learn how to control many of their internal responses very well. Biofeedback can sometimes be an alternative to using medication to reduce tension or pain. Its range of applications has grown tremendously. Here are some examples of its uses: