Thursday February 26 2009
People's personalities are complex and are governed by more than genes
“Variations in a mood altering gene influence whether or not people take a pessimistic or optimistic view of the world,” The Daily Telegraph reported. It said that researchers believe that different versions of the gene can affect whether people tend to have a "sunny disposition" or are drawn to more negative aspects of the world. The newspaper reported that the scientists believe the findings could help develop new treatments for anxiety and depression.
These findings come from a study that looked at the speed of responses of 111 healthy volunteers to good and bad pictures on a computer screen and which version of the gene they had. The study did not look at whether the gene affected people’s responses to real life problems, or their risk of developing mental health problems. People’s personalities, including whether or not they look on the bright side of life, are complex and are likely to be affected by different aspects of their environment as well as genetics. This study has no direct implications for the treatment of people with mental health illnesses.
Where did the story come from?
Dr Elaine Fox and colleagues from the University of Essex carried out this research. The study was funded by the University of Essex and the Wellcome Trust. The study was published in the peer-reviewed journal Proceedings of the Royal Society B.
What kind of scientific study was this?
This experimental study looked at how genetic variations affect people’s responses to positive and negative pictures. The researchers were particularly interested in variations in the serotonin transporter gene. Serotonin is a chemical that is used to transmit 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 region that controls the gene’s activity (called the promoter). The variation exists in a ‘short’ form and a ‘long’ form. A previous study found that carriers of the short form were more likely to develop depression if they experienced traumatic life events. The researchers in the current study wanted to test the theory that the serotonin transporter gene might be related to whether a person focuses on positive or negative material.
The researchers enrolled 111 people who had never been diagnosed with a psychiatric disorder and were not taking medicines that might affect their mental activity. All participants filled in standard questionnaires that assessed their anxiety and depressive characteristics, as well as their personality. Although DNA samples were taken from all participants, data was only available for 97 people, and so only these people were included in the analyses. The DNA was analysed to look at 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.
The researchers then selected 20 positive, 20 negative and 40 neutral pictures from a standard picture set. The participants were shown pairs of these pictures side by side on a computer screen. Each pair had a neutral picture and either a positive or negative picture. Which side of the screen the type of picture was shown varied. The participants were asked to concentrate on a cross in the centre of the screen for half a second before being shown each pair of pictures for another half a second. The pictures were followed by an image of two dots on either the left or right side of the screen. The dots were arranged vertically or horizontally and the participant had to indicate which version of the dots had appeared. In this type of test, the speed at which the participants respond is assumed to be related to which side of the screen they are focusing on. For example, if they are looking at the image on the right, and the dots then appear on the right, response times are expected to be faster than if they had been looking at the image on the left. The researchers therefore took the response times as indicators of which image the participant had been focusing on.
Each participant did 320 of these tests, with 720 milliseconds of a blank screen between each. The researchers carried out statistical tests to look at whether the variant of the serotonin transporter gene each participant carried affected which image they focused on (that is, how long it took them to respond depending on where the dots were located). The researchers calculated a score representing each participant’s bias towards positive or negative images. They did this by subtracting the average reaction time when the dots were in the same position as the emotive picture (positive or negative) from the average time when the dots were in the same position as the neutral picture. A number below zero indicated avoidance of that type of image (positive or negative), a number above zero indicated a preference for focusing on that type of picture, and a score of zero indicated no preference for emotive over neutral images.
What were the results of the study?
The researchers found that there were statistically significant differences in reaction times depending on which variants of the serotonin transporter gene the participants carried, whether a negative or positive picture was shown and the screen position of the dots relative to the positive or negative picture (same side or opposite side).
Participants with two long forms of the serotonin transporter gene showed an avoidance of negative pictures and a preference for positive pictures. For participants with two short forms, or one long and one short form of the gene, there was a tendency towards focusing on the negative and avoiding the positive, but this tendency was not statistically significant.
What interpretations did the researchers draw from these results?
The researchers conclude that people carrying two long copies of the serotonin transporter gene show a strong bias towards paying attention to positive images and avoiding negative images that is not present in people with other genetic make-ups. They suggest that their findings indicate that a “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 people carrying 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”.
What does the NHS Knowledge Service make of this study?
There are a number of points to consider when interpreting this relatively small study:
- Although the researchers found differences in tendency to focus on positive and negative images, they did not find differences in levels of depression, anxiety, neuroticism or extroversion between people of different genetic make-up. Therefore, this study does not show that these variations in a person’s serotonin transporter gene affect these characteristics.
- None of the people in the study had ever been diagnosed with a mental health condition and so the results may not be representative of what would be found in people who do have a mental health condition. The results also do not tell us whether there is a link between the risk of developing a mental health condition and variation in the serotonin transporter gene.
- Different people may interpret images in different ways, so what is assumed to be negative to one person, may not be negative to another. The study did not ask participants to identify whether images were positive, negative or neutral to them, and this complicates the interpretation of the results.
- The researchers report that there are other variations that occur within the serotonin transporter gene promoter that they did not assess.
- There may be differences other than serotonin transporter gene variation between the groups compared that are responsible for the differences seen.
- The differences in attention to positive and negative images may not reflect people’s ability to cope with the stresses of real life.
People’s personalities, including whether or not they look on the bright side of life, are complex and likely to be affected by a variety of environmental factors (such as life events and interactions with others) as well as a variety of genetic factors.