Sally Brown in Therapy Today reports on what neuroscience is discovering about the effects of depression on the human brain and the changes wrought by therapy.
Size of areas in the brain
The hippocampus, part of the limbic system for forming memories and connecting moods to memories is significantly smaller in people who have experienced depression that in healthy brains. And a smaller hippocampus has been associated with executive function impairments, such as learning and memory impairments and poorer treatment response. This research along with other smaller studies confirms that depression reduces the brain size. This may account for ‘brain fog’, a feeling that many people with depression report, including difficulty recalling words and details during conversations. It is thought that the result of a smaller hippocampus in depression is due to a prolonged stress reaction, as there are many receptors in this part of the brain.
The are some indications that selective serotonin re-uptake inhibitors and aerobic exercise can increase neurogenesis in the hippocampus and that’s why they can help people with depression.
Scientists have discovered overactivity in the amygdala, the part of the limbic system that processes emotions, particularly negative emotions. This can begin to explain the ‘mental filter’, common in depression, that overemphasises negative events and emotions. Preliminary research suggests that talking therapies can help to regulate this overactivity. It was found that in patients with an overactive amygdala, after 14 weeks of therapy this reduced and there was an increase in activity in the prefrontal cortex, an area responsible for planning and self-control.
Additionally, overactivity in the anterior cingulate cortex has been found in people with social anxiety and those who experience a punitive inner voice in depression and this links to the importance of addressing inner conflicts within therapy.
There is a genetic influence on susceptibility to depression. In 2003 Dr Avshalom Caspi and Colleagues found people that have a variation of the serotonin transporter gene, known as a ‘short allele’ are at a much highter risk that those with a ‘long allele’. These are in charge of the ability to suppress things that are emotionally painful, and those with the long allele are better at ignoring painful feelings. We now know that there is a considerable interaction between genes and environment, so helping people to manage their sensitivity to emotional pain in counselling can have a epigenetic effect.
An imbalance in brain connectivity could explain a continuous sense of loss and disappointment in depression as there seems to be enhanced connectivity between the ‘non-reward’ areas of the brain in depressed people, which is activated when we experience disappointment, punishment and is associated with our sense of self. At the same time there is a reduction in connectivity of the ‘reward’ areas, associated with memory. This may account for why depressed people feel overwhelmed by small disappointments and struggle to recall happy memories.
Cause or Effect?
There is no ‘typical’ experience of depression or one-size-fits-all treatment and the complexity of neuroscience findings back this up. Our relationship to ourselves, others and the world is a dynamic process and accompanied by complex interactions in the brain, hence there are multiple possible causes of depressive symptoms and often they are understandable reactions to difficult life situations.
We don’t know if these changes are the cause or consequence of depression and it might be that some changes are compensatory and protect the brain from damaging effects of depression.
What the article highlights is that the social, biological and psychological models of mental illness don’t need to be divided categories, but are permeable and are inter-related.
What is important to note is that the brain’s plasticity continues throughout life, so nothing is fixed. Neural pathways can be strengthened and those that are outdated and unhelpful ways of thinking can be weakened, but in whatever form, change through counselling is always possible.
A way that I like to visualise this is that in depression our neural pathways leading to automatic unhelpful thoughts might be currently like a motorway – strong and engrained, a well travelled path. Through therapy we try to start encouraging the A roads running next to the motorways to start to be used and become a more valid option. This might take some work at first and require a conscious effort to be aware of your possible choices and make such changes, but as the road strengthens these more helpful ways of being will become stronger and more automatic.