Metastasis is a concept associated with cancer. When this disease strikes a particular location in the body it can, when sufficiently mature, spread to other organs systems and become systemic, a process known as metastasis. The salient feature of this condition is that treating the original site of the disease no longer cures the condition. For instance, if the disease started in a kidney, metastasised, and then the affected kidney was removed the disease would continue anyway.
Is clinical depression like this? Depression has a natural and normal function and is a response to a wide range of conditions. After an interval of days to weeks the condition eases. Addressing the original cause of the depression also relieves the condition. But if it persists for some time then it can spread and become ‘systemic’ and so affect every part of the person’s life to the point that addressing the original cause no longer cures the condition. We see this in major depression-related mental disorders, for instance, to PTSD or initiated by the loss of a loved one, loss of employment and so on.
What makes major depression challenging to treat is the fact that any of the symptoms of depression could be the original cause and depression that has metastasised will eventually become systemic, that is, have the appearance of almost all causes of depression. Sleep disturbances, lethargy, a difficult upbringing, negative thinking, relationship problems, lack of opportunity, bad luck, physical problems including such things as allergies, discrimination and so on can all be causes of depression and/or symptoms in that a person with systemic (major) depression will, upon being asked, relate experiences or conditions in all these domains consistent with the depression they experience as if all of these are contributing causes.
Such a patient may be able to identify a period before major depression and therefore also identify the cause of the natural depression at the root of their condition. But addressing this original cause may no longer relive the general condition and the individual will start to recall more possible original causes or further consequences, properties or conditions relating to the original cause that have not been addressed. The reason for this behaviour is the dual nature of major depression in that any of the symptoms can be a cause and when depression becomes systemic the brain reconfigures memories to become more consistent with the current condition.
To understand how this works we can recall the famous experiments done by Wilber Penfield on patients undergoing open brain surgery to treat epilepsy. Typically, the brain is probed with electrical stimulation to more accurately identify the exact location of particular brain areas. When an area associated with humour was stimulated a patient burst out laughing. When asked why she laughed she said ‘You guys, you are just so funny!’ In other words the order of causation had been reversed: the usual ‘laugh in response to a joke’ was triggered part way through so that the brain simply appended the joke to the recollection. Neuroscientists call this process ‘confabulation’ and it was observed most prominently in experiments on ‘split brain’ patients, those who had had the corpus callosum severed. Typically, the more verbose left side of the brain will confabulate when information is provided only to the right side of the brain and communication of vague general emotion is all the left side is aware of.
Systemic (major depressive disorder) depression functions just like this. The depression and associated feelings are experienced regardless of the current condition and so the brain projects the feeling onto the current (or any, including recalled) condition and interprets it as if the current condition was the cause of the depression. This has the unfortunate consequence of obscuring the actual cause. It is also notable that when depression becomes systemic and various confabulated causes emerge, even though confabulated these now become real causes of the depression. For instance, if a person had a particularly challenging upbringing then this may contribute to the depression. But if a person suffers systemic depression for some other reason then they may recall a challenging upbringing by overemphasising any negative events and suppressing the positive. This ‘challenging upbringing’ now contributes to the depression. The process reinforces itself and makes the overall condition worse.
As part of the confabulation process, which is typically a non-conscious process which the individual is unaware of, involves the thinking process, changing that thinking process with consciously mediated overriding thoughts can help, changing the underlying mood with medication also helps. Addressing some of the typical causes or contributors to depression such as sleep problems, lack of exercise, lethargy and false recollections also help to reverse the depression.
Metastasis of cancer may well be a good analogy for the progression from normal depression, which everybody experiences as a normal part of being human, to the major depressive disorder, systemic depression, which is the disabling condition requiring extended psychiatric treatment.