Washington, Jan 15 (IANS): Why is that some people fear piercing of a needle while others even brave complex surgeries with a smiling face.

Scientists now have an answer. According to them, the secret lies in the amount of grey matter in the brain.

Researchers at Wake Forest Baptist Medical Centre in North Carolina in the US have shown that how intensely people perceive pain is related to the structure of the brain.

“We found that individual differences in the amount of grey matter in certain regions of the brain are related to how sensitive different people are to pain,” said Robert Coghill, professor of neurobiology and anatomy at Wake Forest Baptist.

Conducting the study on 116 healthy volunteers, the researchers heated a small spot of skin on their arm or leg to 120 degrees Fahrenheit and tested their pain sensitivity.

The scientists then recorded the images of the volunteers' brain structure with the help of MRI scanning, said the study published in the journal Pain.

“Subjects with higher pain intensity ratings had less grey matter in brain regions that contribute to internal thoughts and control of attention,” said Nichole Emerson, a graduate student in the Coghill lab and first author of the study.

These regions include the posterior cingulate cortex, precuneus and areas of the posterior parietal cortex, she said.

Areas of the posterior parietal cortex play an important role in attention. Individuals who can best keep their attention focused may also be best at keeping pain under control, Coghill said.

The brain is made up of both grey and white matter. Grey matter processes information much like a computer, while white matter coordinates communications between the different regions of the brain.