By monitoring activity levels in the human brain's prefrontal cortex, the researchers demonstrate for the first time that people who have more activity in the left side of this area also have a stronger immune response against disease. The findings, soon to be published in the online edition of the journal Proceedings of the National Academy of Sciences, pinpoint one of the mechanisms underlying the link between mental and physical well-being.
Numerous scientific studies show that keeping a positive attitude can keep a person healthy, says Richard Davidson, a UW-Madison neuroscientist and senior author of the paper. But he adds that the reasons why this connection exists are poorly understood.
By turning to the brain - an organ that sends signals that guide emotional response - Davidson and his group have identified one possible explanation: activity in the prefrontal cortex, a region of the brain long associated with affective style, or how a person responds emotionally to an event.
"Emotions play an important role in modulating bodily systems that influence our health," says Davidson. "We turned to the brain to understand the mechanisms by which the mind influences the body."
While earlier studies have linked emotional and physical health, as well as brain activity and affective style, Davidson says none have established a direct link between brain activity and immune function.
The latest study by the UW-Madison group demonstrates this connection.
For the study, the researchers worked with 52 individuals between the ages of 57 and 60 who were recruited from the Wisconsin Longitudinal Study - a long-term study of more than 10,000 people who graduated from Wisconsin high schools in 1957. Specifically, the scientists wanted to know if people who showed more activity in the left side of the prefrontal cortex - a part of the brain associated with positive emotional responses - also showed greater immunity to the influenza virus after vaccination.
To answer this question, the researchers vaccinated all the subjects against the flu virus. Before vaccination, they measured the study participants' brain activity, both at a baseline state and during emotion eliciting memory tasks. During these tasks, the participants were asked to recall two events - one that made them feel intensely happy and another that left them feeling intensely sad, fearful or angry. As the respondents focused on the emotion experienced for one minute, the researchers measured the electrical activity in both the right and left sides of the prefrontal cortex.
Previous studies, notes Davidson, have shown that individuals with greater activity on the right side of this brain region tend to have a more negative affective style, which can cause these individuals to respond inappropriately to emotional events.
The researchers collected these prefrontal cortex activity levels again after the subjects spent five minutes writing about the particular events. At this time, they also measured the participants' eyeblink reflex in response to sudden noises. This measure, explains Davidson, provides a convenient and objective way to measure how negatively or positively a person reacts to a stimulus.
Three times in the six months following vaccination, the researchers collected serum samples from each subject to track the number of flu-fighting antibodies in the blood, which can determine immune function.
Six months after being vaccinated against the flu virus, the subjects who had greater activity in the left side of the prefrontal cortex, instead of the right side, also had a greater rise in the number of antibodies for influenza, says Davidson.
"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," says the Wisconsin researcher. "It begins to suggest a mechanism for why subjects with a more positive emotional disposition may be healthier."
This research was supported by grants from the National Institute of Mental Health and the John D. and Catherine T. MacArthur Foundation Research Network on Mind-Body Interaction.
- Emily Carlson, 608-262-9772, firstname.lastname@example.org