If relatively simple animals like rats could achieve such a remarkable level of internal control, Miller figured, couldn't human beings, with their greater intelligence, regulate more of their bodily processes? After these early revelations, many scientists found that information about the autonomic nervous system could be fed back to a person as 'biofeedback' to pinpoint where a person should send intention to his body.

In the 1960s, John Basmajian, a professor of medicine at McMaster University in Ontario and a specialist in rehabilitative science, began training people with spinal-cord injuries to use electromyography (EMG) feedback to regain control over single cells in their spinal cord (Basmajian JV. Muscles Alive: Their Functions Revealed by Electromyography. Baltimore: Williams & Wilkins, 1967).

At roughly the same time, psychologist Elmer Green at the Menninger Institute in Topeka, Kansas, pioneered a method of bio-feedback to treat migraine headaches that is now an accepted form of therapy for the condition (Psycho-physiology, 1969; 6: 371-7; J Transpers Psychol, 1970; 2: 1-26).

Biofeedback is especially useful for treating Raynaud's disease, a vascular condition in which the blood vessels of the extremities are constricted when exposed to cold, causing the fingers and toes to grow cold, pale and even blue (Biofeedback Self-Regul, 1987; 12: 257-72).

During biofeedback treatment, a patient is hooked up to a computer. Transducers applied to different parts of the patient's body send information to a visual display, which registers activities of the autonomic nervous system such as brainwaves, blood pressure and heart rate, or muscle contractions. The audio or visual information fed back to the patient depends on the condition; in the case of Raynaud's, as soon as the arteries to the hands constrict, the machines record a drop in skin temperature and a light bulb flashes or a beeper sounds. This feedback prompts the patient to send an intention to his body to adjust the process in question; in the case of Raynaud's, the patient sends an intention to warm up his hands.

Since those early days, biofeedback has become well established as a therapy for virtually every chronic condition, from attention-deficit/ hyperactivity disorder (ADHD) to menopausal hot flashes. Stroke patients and victims of spinal-cord injuries now use biofeedback to rehabilitate or regain the use of paralyzed muscles. It has even proved invaluable in eliminating the pain felt in a phantom limb (Am J Clin Biofeed, 1982; 5: 150-3). Even astronauts have used biofeedback to cure motion sickness while journeying to outer space (Aviation Space Environ Med, 1987; 58: 34-41).

The more conventional view of biofeedback maintains that it has something to do with relaxation-learning to calm down the fight-or-flight responses of our autonomic nervous system.

However, the sheer breadth of control would argue that the mechanism has more to do with the power of intention. Virtually every bodily process measurable on a machine-down to a single nerve cell controlling a muscle fibre-appears to be within an individual's control. Volunteers in studies have achieved total mental mastery over the temperature in their bodies (Psychother Psychosom, 1988; 50: 22-8) and even the direction of blood flow to the brain (Am J Psychiatry, 1981; 138: 1182-7).

Hypnotherapy
Hypnosis can be used as a type of healing intention-an instruction to the brain during an altered state. Hypnotists continually demonstrate that the brain or body is particularly susceptible to the power of directed thought when under subconscious direction.