Anxiety and depression: similarities and differences in the brain
Anxiety and depression have to date primarily been studied as separate psychiatric disorders, whilst they often occur in combination. Marie-José van Tol has has discovered that there is an overlap in the activity and volume of parts of the brain in anxiety and depression, but that both disorders have unique characteristics. PhD defence with honours 26 May.
Some 30% of people who suffer depression also have an anxiety dsorder (such as a social anxiety, panic or generalised anxiety disorder); half of those with an anxiety disorder will at some time in their life experience depression. A combination of anxiety and depression is known as a 'comorbid disorder'. A great deal of research has already been done using MRI scans on people with depression and on people with an anxiety disorder, but they have never been combined in one study that also includes a group suffering from a comorbid disorder. Van Tol's study included all three groups.
Van Tol discovered in the literature that depression and anxiety appear to share abnormalities in the brain. This could explain their high comorbidity. Van Tol was the first to find evidence that people with anxiety and depression really do share certain abnormalities, for example, a reduced volume in the area of the cingulate cortex that is important in regulating emotions. Furthermore, anxiety and depression are each related to unique abnormalities in the volume of particular parts of the brain.
In her research Van Tol investigated whether people with depression or an anxiety disorder process and remember positive and negative information differently. The study showed that these individuals' memory is no worse, but that they incorporate positive information less quickly than individuals without this disorder. This may be the result of reduced hippocampal activity.
What was remarkable was that the effect also occurred in individuals who, at the time of the study, were suffering no obvious effects from their disorder, or their comorbid disorder. This could be an indication that people remain vulnerable to possible relapse. The effect was apparent independently of the seriousness of the disorder and whethre or not the person was taking medication. In processing negative information no difference was perceived in the hippocampus between individuals with or without a disorder. There are indications that negative events can have an added adverse effect on a depressive mood, as processing negative information goes hand-in-hand with a higher level of activity in the amygdala.
Van Tol also looked at the functioning of the pre-frontal cortex during while a non-emotional, cognitive task was abeing carried out; it is assumed that people suffering from depression are less skilled in such activities as maintaining and dividing their attention, actively suppressing disturbing information from the environment and implementing plans. The results demonstrate that ptople suffering from depression activate the dorsolateral prefrontal cortex more than people without a disorder in order to achieve the same performance. This increased activity was not observed in people who had no symptoms at the time of the tests, in people with a comorbid disorder and people with only an anxiety disorder.
Van Tol also calculated that the correlation between the actvity of all the brain areas in people suffering from depression but who were free of medication, but without an anxiety disorder, and a healthy control group. Th results show that in individuals suffering depression the communication between the frontal cortex and the subcortical structures is less effective. This seems to be related to the processing of positive information. It might be that their mood is no longer positively influenced by pleasurabl activities, because the structures do not communicate optimally.
Van Tol had already discovered that emotional abuse in childhood results in stress that in turm causes impaired developmwnt of the medial prefrontal cortex. As a result, the likelihood of depression and anxiety disorders in later life may be greater than for children who do not suffer emotional abuse. Finally, Van Tol also discovered that in healthy, more extravert individuals the volume of particular areas of the brain, the amygdala and the orbito-frontal cortex, are greater than in less extravert people.
These findings give an insight into how such factors as personality and early emotional experiences increase the likelihood of developing a depressive or anxiety disorder later in life.
Marie-José van Tol's study is part of a broader research project, the Netherlands Study of Depression and Anxiety (www.nesda.nl), being carried out by the University Medical Centres of Leiden and Groningen and the Vrije Universiteit in Amsterdam. This MRI study involved a very large population of 301 patients.(31 May 2011)