Whether you see a glass half-empty or half-full may depend on your genes, report scientists in Britain.
Variations in a mood-altering gene influence whether people take a pessimistic or optimistic view of the world, Elaine Fox and her colleagues at the University of Essex believe. They found that different versions of the gene, which is involved in the transportation of the wellbeing chemical serotonin, affect whether or not we are drawn to negative or positive aspects of the world.
Serotonin is a chemical that transmits messages between nerve cells in the brain (a neurotransmitter), and the transporter moves serotonin into the nerve cells. The serotonin transporter gene is known to have a variation in the part of the brain that controls the gene's activity (a promoter). The variation exists in 2 forms: a 'short' form and a 'long' form.
A previous study found that people who carry the short form are more likely to develop depression if they experienced stressful events in their lives. Those with a long version of the gene tend to have a "sunny disposition", dwelling on positive aspects of life and deliberately playing down the negative aspects. The scientists in the current research wanted to test the theory that the serotonin transporter gene might be related to whether a person focuses on positive or negative material.
The psychologists also believed that the findings could help develop new treatments for anxiety and depression. They came up with the results after taking DNA samples from 97 volunteers and then subjecting all those people to a dot-probe paradigm test. The DNA was analyzed in order to establish whether participants had the long or short form of the 'serotonin transporter gene promoter'. All humans have two copies of the gene, and can therefore carry two short forms, two long forms or one of each.
In a dot-probe paradigm test all the study participants were shown 20 positive, 20 negative and 40 neutral pictures from a standard picture set. The participants were briefly shown pairs of these pictures side by side on a computer screen. Each pair had a neutral picture and either a positive or a negative one.
After that they had to press a keypad to indicate when a dot has appeared on the screen. It has been known for quite a certain time that the more distracting an image is, the longer it takes for a person to react and respond when the dot appears. All this allowed the experts to figure out how distracting particular people found particular images.
The results showed that there were significant differences in reaction times depending on which type of the serotonin transporter gene the participants carried. Those adults with the longer version of the gene averted their gaze towards positive images, such as sweets and sailing boat, while participants with 2 short forms were prone to looking at the negative photos, such as spiders.
The psychologists believe that people carrying two long copies of the serotonin transporter gene tend to pay attention to positive images and avoid negative images that is not present in people with other genetic make-ups. According to the researchers, the results of the study suggest that "genetically driven tendency to look on the bright side of life is a core cognitive mechanism underlying general resilience to general life stress".
They say that the absence of this tendency in individuals with the short form of the gene "is likely to be linked with the heightened susceptibility to mood disorders such as depression and anxiety that has been reported in this group".