Advances in the scientific study of pain could provide crucial insights into how consciousness relates to the body and the self, according to Richard Chapman of Washington University.

Professor Chapman said that pain was an "intrinsically subjective, unpleasant sensory and emotional experience" which people associated with tissue damage. Neurology alone was often insufficient to explain the many phenomena associated with pain or its conspicuous absence despite obvious tissue damage and trauma. He argued that this called for a questioning of our conventional understanding of mind and body.

Clinicians were often faced with deep questions concerning the mind and body, said Professor Chapman. One classic example was the emergence of a "phantom limb" in patients who have had that limb amputated.

Professor Chapman said that there were many cases of patients who lose limbs or other parts of their body and yet retain a vivid awareness of the lost part. And sometimes phantom body parts hurt and were resistant to all forms of treatment.

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He said that research into memories that patients have under general anaesthesia suggested multiple levels of brain processing somehow disassociated from waking consciousness.

"Some drugs do not block the immediate awareness of pain but prevent explicit or episodic memory of it. These and other problems make mind-body issues a part of everyday pain clinic work," he said.

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Deep questions about the relationship of mind to body were raised outside the laboratory or hospital. Professor Chapman cited fakirs who pierce their skin and exhibit dramatic tissue trauma and yet deny pain verbally and express no kind of pain behaviour. There were also certain religious ceremonies which involved dramatic tissue damage to subjects with no discernible pain. Another example was of soldiers in combat who sustained major injuries without pain.

Professor Chapman said that many clinicians still thought of pain as a sensation, ignoring its emotional features. Recent brain imaging studies highlighted the importance of the emotional impact of pain (stimulation of the limbic system) as well as the sensory (stimulation of the sensory cortex). "The complexity of pain challenges researchers to build a broader basis for its understanding," he said.

He said that integrating insights into the emotional, sensational and cognitive dimensions of pain with theories on the nature of consciousness could assist pain research enormously, adding that on the other hand, the pain research field was a fertile ground for scientific inquiry into the nature of consciousness.