Scientists trying to find whether there is any truth to "mind over matter" say brain activity can control resistance to influenza. They have demonstrated a direct link between the brain's emotional state and the body's immune defences to explain why depressed people are more likely to catch a cold.
Although there is considerable research showing a person's mood can influence their susceptibility to a virus, no previous study has found a direct link to the brain.
Neuroscientists led by Richard Davidson, of the University of Wisconsin at Madison, found electrical activity in the left prefrontal cortex - the region of the brain above the left eye - appears to play a critical role in directing the body's immune system.
High levels of activity in the same region of the brain are known to be linked with a more positive attitude to life, with severely depressed people having a particularly subdued left prefrontal cortex relative to their right prefrontal cortex.
Professor Davidson's findings are published in the Proceedings of the National Academy of Sciences. They checked 52 volunteers witha brain scanner, measured each person's electrical activity in the left and right pre-frontal cortex before injecting them with a flu vaccine to see how well their immune systems responded to a simulated viral attack.
Over the next six months, the scientists monitored the levels of flu-fighting antibodies that appeared in the blood of each volunteer. They found those with relatively high levels of activity in the right pre-frontal cortex produced greater amounts of flu antibody.
"This study established that people with a pattern of brain activity that has been associated with a positive affective style are also the ones to show the best response to the flu vaccine," Professor Davidson said. "It begins to suggest a mechanism [that means] subjects with a more positive emotional disposition may be healthier."
Scientists have demonstrated there is a link between pyschological wellbeing and physical health. Severe stress and depression also have a direct impact on the immune system, affecting chemical messengers called cytokines, which are needed to recover from an infection. Professor Davidson added: "Emotions play an important role in modulating bodily systems that influence our health."
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