Research in the United States has revealed that the part of the brain that controls happy emotions can stimulate the immune system to work harder, explaining much of the mind’s remarkable influence over the health of the body.

The study, at the University of Wisconsin-Madison, found that particular patterns of activity in the brain’s prefrontal cortex, the section that processes emotion, were linked to strong or weak immune responses to infection. People who have high activity in the left side of the prefrontal cortex, the side associated with positive thinking, have much stronger immune systems than those with greater activity on the right side, which deals with more negative emotions.

The findings offer one of the best explanations yet for a phenomenon that doctors have observed for many years: that people with an optimistic, happy-go-lucky approach to life tend to be healthier than those who are always miserable. Although some of this effect is known to be linked to stress, which produces hormones that can suppress the immune system, the new research highlights a more direct mechanism by which the mind has power over matter.

Richard Davison, the neuroscientist who led the study, said it was the first to show a direct link between brain activity and the body’s defences. “Emotions play an important role in modulating body systems that influence our health,” he said. “We turned to the brain to understand the mechanisms by which the mind influences the body.” Numerous studies have shown that people who think positively tend to become ill less frequently, and to recover more quickly, than those with a more negative attitude.

A recent paper by psychologists at Yale University, for example, found that people over 50 who thought positively about ageing lived for an average of 7½ years longer than those who did not. Research at Brigham and Women’s Hospital in Boston also found improved lung function in men who had an optimistic take on life.

Other studies, however, have found no link: a recent investigation by the Medical Research Council found that cancer patients’ attitude to coping with their illness had no influence on survival rates.

In the Wisconsin research, details of which are published today in the journal Proceedings of the National Academy of Sciences, Dr Davidson’s team studied 52 volunteers aged between 57 and 60. The subjects were asked to recall two events in turn, one that had made them feel intensely happy and one that had provoked feelings of sorrow, fear or anger.

While they focused on these emotions for a minute at a time, the scientists used an electroencephalogram to measure electrical activity in both sides of the brain’s prefrontal cortex. The readings were used to establish which side of the prefrontal cortex each person tended to favour.

Further evidence of brain activity was collected as volunteers spent five minutes writing about the events. They were also given a “startle reflex” test, measuring how quickly their eyes blinked in response to sudden noises.

The study group were then given an influenza vaccination, and their immune response to this was assessed three times over six months through measurement of blood antibody levels.

The results showed that the most positive thinkers, with the highest levels of activity in the left prefrontal cortex, had by far the strongest immune response. The most intense negative thinkers had poorer immune responses, and a more pronounced startle reflex.

“This study establishes 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,” Dr Davidson said. “It begins to suggest a mechanism for why subjects with a more positive emotional disposition may be healthier.”

Always look on the bright side of life

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