Monday, October 31, 2005

"Mirrors can trick the brain into recovering from persistent pain"

Looking in a mirror at a reflection of their healthy hand could help people with persistent pain ease their symptoms and eventually overcome their problem, say scientists in the latest edition of the journal Clinical Medicine.

The treatment, being developed by researchers from the University of Bath and the Royal National Hospital for Rheumatic Diseases (RNHRD), is based on a new theory about how people experience pain even when doctors can find no direct cause.

This ‘cortical’ model of pain suggests that the brain’s image of the body can become faulty, resulting in a mismatch between the brain’s movement control systems and its sensory systems, causing a person to experience pain when they move a particular hand, foot or limb.

Researchers believe that this kind of problem could be behind a host of pain-related disorders, such as complex regional pain syndrome and repetitive strain injury....

“We think it is the same system that is triggered when you are running down stairs, miss the last step and then feel a jolt of surprise.

“In missing that bottom step, you jar the prediction that your brain had made about what was going to happen, triggering an alert to the body that things are not as you expected, hence the feeling of surprise.

“This is because in most cases normal awareness and experience of our limbs is often based on the predicted state rather than the actual state.

“When the two do not match we think sensations are generated to alert the body that things are not as it thought – rather like an early warning mechanism.

“If the discrepancy is very large [like in the mirror experiment described below] then pain may be experienced, as pain is the body’s ultimate warning mechanism....

In a separate study published in the journal Rheumatology earlier this year, researchers from Bath, Cardiff and Exeter showed that it is possible to create sensations and feelings in one limb by looking at a reflection of the other limb in a mirror.

They asked 41 healthy people to sit with a mirror at right angles in front of them so that they could only see one side of their body at a time.

The volunteers were then asked to move their limbs in the same direction at the same time, and then in opposite directions whilst viewing the mirror reflection of one hand.

Within 20 seconds of starting, more than two thirds of people involved in the trial reported some kind of sensation in their hidden limb when the movement they were seeing in the mirror was different to what they were feeling in the hidden hand, for example by moving their hands in different directions.

These sensations included numbness, pins and needles, a change in temperature and moderate aching, despite receiving no neural damage to that limb....

“It would appear that innate susceptibility plays a part, with some individuals more vulnerable to, or simply better at detecting, these sensations.”

More @ the University of Bath

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