[dropcap]T[/dropcap]HE link between mind and body is terrain into which many medical researchers, fearing ridicule, dare not tread. But perhaps more should do so. For centuries, doctors have recognised the placebo effect, in which the illusion of treatment, such as pills without an active ingredient, produces real medical benefits. More recently, respectable research has demonstrated that those who frequently experience positive emotions live longer and healthier lives. They have fewer heart attacks, for example, and fewer colds too.
Why this happens, though, is only slowly becoming understood. What is needed is an experiment that points out specific and measurable ways in which such emotions alter an individual’s biology. And a study published in Psychological Science, by Barbara Fredrickson and Bethany Kok at the University of North Carolina at Chapel Hill, does precisely that.
Dr Fredrickson and Dr Kok concentrated their attentions on the vagus nerve. This nerve (illustrated right, in an early anatomical drawing) starts in the brain and runs, via numerous branches, to several thoracic and abdominal organs including the heart. Among its jobs is to send signals telling that organ to slow down during moments of calm and safety.
How effectively the vagus nerve is working can be tracked by monitoring someone’s heart rate as he breathes in and out. Healthy vagal function is reflected in a subtle increase in heart rate while breathing in and a subtle decrease while breathing out. The difference yields an index of vagal tone, and the value of this index is known to be connected with health. Low values are, for example, linked to inflammation and heart attacks.
What particularly interested Dr Fredrickson and Dr Kok was recent work that showed something else about the vagal-tone index: people with high tone are better than those with low at stopping bad feelings getting overblown. They also show more positive emotions in general. This may provide the missing link between emotional well-being and physical health. In particular, the two researchers found, during a preliminary study they carried out in 2010, that the vagal-tone values of those who experience positive emotions over a period of time go up. This left them wondering whether positive emotions and vagal tone drive one another in a virtuous spiral. They therefore conducted an experiment on 65 of the university’s staff, to try to find out.
They measured all of their volunteers’ vagal t