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Pain waves-tolerance linked to brain


Pain tolerance linked to brain

Whether it's childbirth or a broken leg, why can some people "grin and bear" a painful experience while others find the agony overwhelming?

The answer may have less to do with how wimpy or heroic we are, and more to do with inherent variations in the way our brains respond to pain.

That's the conclusion of a new study showing that remarkable individual differences exist in our sensitivity to pain. The report confirms a long-held hunch that pain-fighting chemicals called opiates in the brain are at the heart of these highly personal variations.

In a ground-breaking study, American researchers managed to convince volunteers to subject themselves to a painful experience for 20 minutes, and at the same time, have their brains scanned using positron emission tomography or PET.

The pain was triggered by injecting a concentrated salt-water solution directly into each volunteer's jaw muscle - a technique thought to mimic the chronic pain of a condition called temporo-mandibular joint disorder.

Radioactive traces molecules were injected into the subjects' blood stream so that only parts of the brain involved in producing or responding to opiates showed up in the imaging process.

Even though the experiment was carefully designed to ensure the pain stimulus was the same for each person, the scientists found dramatic variations in brain responses that matched well with ratings of pain the volunteers gave.

The greater the activation of the brain's anti-pain response, the easier the pain was to bear.

The researchers say the differences stem both from amount of opiates the brain produces, and the number of receptors or docking sites present. It's the interaction of the opiate molecules with their specific receptors that allows them to do their job.

The results might explain some annoying conundrums, such as why some women can apparently breeze through childbirth while others are calling for a full anaesthetic as soon as they reach the labour ward.

Or why some of us can endure painful conditions like arthritis, while others find themselves crippled by something as trivial as an insect bite.

The research, published in today's Science, could also provide insights into the effectiveness of pain medications and the development of chronic pain.