Biofeedback teaches people how to exert conscious control over various conditions which involve stress or pain. Instruments measure certain functions such as blood pressure, muscle tension and brain wave activity. The patient learns how to recognize areas of dysfunction which involve these activities and how to control them. By observing the fluctuations of a body function - for example, breathing, heart rate or blood pressure - you can learn eventually how to adjust your physical reactions and thoughts/emotions in order to change the body's response. It is possible to learn to control pain, blood pressure, heart rate, insomnia, and migraines to mention just a few conditions. This has been practiced with yoga and meditation techniques for thousands of years and now is widely accepted in the US by both conventional and alternative practitioners. Biofeedback may involve intangibles such as meditation, but is usually combined with instruments controlled by the patient.