Can someone tell me about Biofeedback?!

Can someone tell me about Biofeedback?

I do not mean the natural biochemical biofeedback mechanism that occur in the body.

I am referring to the alternative medicine thing a me that started in the 70's as a way of - well using the bodies natural mechanisms to controll certain automatic functions in the body or something like that.

Biofeedback was a method to see how the body reacts to different states of mind or stress. The goal was to learn what methods of relaxation actually worked for an individual.
There is usually a device that provides a readout of responses through a sensor attached to the skin. It's called galvanic skin response. Temperature is also used as a measure of response.
The higher the stress level, the temperature goes down. With galvanic skin response, the sensor plates are attached to the fingers. The readout is usually a signal. The goal is to make the signal change. First you get a baseline signal; then you think a thought or do a relaxation meditation. If the stress level goes down and the method was successful, the signal should get lower.
I still own a biofeedback device. It still works. The interesting thing is that each person is different. One type of thought might not induce the same response across different people.