Scientists investigate how genetic factors influence depression
French researchers have been investigating the amygdala, a part of the brain that is hyperactive in individuals who suffer from anxiety and depression, and have found that genetic factors have an influence on patient's cerebral activity.
Although scientists have long known that anxiety and depression are caused by psychological and environmental factors, and are often influenced by genetic factors too, it remains unclear just how much each factor affects the onset of anxious and depressive symptoms.
Writing in the journal Human Brain Mapping, the team shows that the brain's activity can be modulated depending on the subject's genetic makeup, personal history and cognition. Their findings suggest that the effects of psychotherapies on the cerebral activity of patients could vary according to their genetic traits.
This work builds on several previous studies that point to the possibility that the 5-HTTLPR gene, a gene that influences serotonin - a substance involved in emotional regulation - could play an important role in depression onset. By looking at the 5-HTTLPR's promoter, a regulatory region of DNA located near the gene it transcribes, the team saw that when the promoter was prevalent in its short form, it accentuated the emotional impact of stressful events.
Scientists now believe that the short form of the gene triggers a more intense activation of the amygdala and therefore can lead to symptoms of anxiety or depression, as the amygdala is involved in emotions and in the recognition of danger signals.
To move forward research, the French team studied the impact of psychological and environmental factors on the 'genetic' effect by carrying out functional magnetic resonance imaging (MRI) brain scans on 45 healthy individuals, including carriers of both the short and long form of the gene.
During these MRI scans, the subjects were shown photographs of pleasant and unpleasant images, and were asked to indicate whether they found the effect of seeing the image to pleasing or not, and to think about the links between the images and themselves.
The results showed a significant disparity between those who carried the short form of the gene and those who did not. Short form carriers showed a higher activation of the amygdala when associating a photo with themselves than when deciding whether an image was pleasing or displeasing. In subjects who didn't possess the gene, the opposite effect was noted.
This means activity of the amygdala varies according to both the form of the gene as well as the type of mental activity being carried out, i.e. whether the activity is objective or linked to the individual on a personal level.
Before the team carried out the scans, they interviewed the test subjects to find out about any negative events that may have occurred in their lives in the past year. The results show that any stress experienced throughout the year also had an effect on the influence of the gene on the activation of the amygdale.
The study therefore shows that brain function is affected by both genetic factors and personal history and psychological conditions. In addition, the team noted forms of psychotherapy such as cognitive therapy can have a diverse range of cerebral effects depending on certain genes.
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Document Reference: Lemogne, C. et al. (2011) Cognitive appraisal and life stress moderate the effects of the 5-HTTLPR polymorphism on amygdala reactivity. Human Brain Mapping. DOI:10.1002/hbm.21150
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