Biofeedback has been used in medicine on and off again for a while. It's hard to learn how to control processes in your body for which you have no feedback. But

Biofeedback has been used in medicine on and off again for a while. It's hard to learn how to control processes in your body for which you have no feedback. But if you're hooked up to a machine which gives you feedback you can learn to control things we usually think of as beyond our will. You can learn to control your heartbeat at will. Migraine sufferers can learn to draw blood into their hands and relieve the migraine symptoms. But it's not clear exactly what's relieving the symptoms, the type of brain activity necessary to control blood flow or the blood flow or both or perhaps neither. That among other things is why it's not established medical practice.