Continuous remodeling of the nervous system that can occur in response to repeated pain stimuli.

"When you cross your arms these maps are not activated together anymore leading to less effective brain processing of sensory stimuli including pain being perceived as weaker" he said in a statement.

People who produce lower amounts of the brain molecule neuropeptide Y (NPY) had "measurably stronger brain responses to negative stimuli and psychological responses to physical pain," the study said.