What makes depression so painful?

What is it that makes depressive disorder so painful?

Thoughts, memories and emotions – are physical. They are particular patterns of activity in particular brain cells (neurons), and, with the right sort of brain-scanning equipment, you can actually see them in the brain. In this way they are exactly the same as physical sensations.

Indeed, one way to look at depression is to think of it as – literally – a type of pain.

Ordinary pain – the sort you get when you stub a toe – is produced by a particular area of the brain. It is called the anterior cingulate cortex, and it is a tiny bit of grey matter which nestles in the deep groove that divides the left and right hemispheres. A pain in the toe also involves other areas of the brain – bits that identify the type of pain, and the location of the injury – but it is the anterior cingulate cortex that makes us register it consciously. This has been shown by brain-scanning experiments. For example, there is a condition called “silent angina”, which differs from “ordinary”, painful angina in that patients do not have pain. Their heart arteries contract in the same way as other angina patients, but instead of feeling the chest pain that warns the others to rest, they feel nothing. Naturally, silent angina is more dangerous than ordinary angina because people who have it do not get a pain “alert” when their body is at risk. Brain scans of “ordinary” and “silent” angina patients show that the only physical difference between them lies in their brains. In the first, the contraction of the arteries produces activity in the anterior cingulate cortex. In the others it does not. This (and other experiments) strongly suggests that pain – the conscious feeling of “ow!” – is generated here.

So how does this relate to “painful” emotions? Well, it seems that emotional pain is generated in just the same way as any other type. Researchers at the University of California in Los Angeles observed activity in the brains of a group of volunteers who had been duped into thinking that they had been intentionally left out of a ball-throwing game. The researchers compared the brain activity with that in another group who had been left out of the game – but in their case it had been made clear that the other players did not want to exclude them. In other words, the first group were feeling “hurt” while the others were not. The difference between them? In the first group the anterior cingulate cortex was active. In the second it was not. The “pain” of social humiliation was generated in precisely the same way as the pain from a physical injury.

Going back to pain caused by physical injury – the angina example shows that sometimes the brain fails to produce pain when it would be useful for it to do so. Conversely, the brain can produce pain that has no source. The clearest example of this is phantom limb pain. People who have had a limb amputated often continue to feel sensations that seem to come from their missing part, sometimes for years after it has gone. Obviously, the pain is not “in” the amputated limb — it is being generated in the brain. The brain areas which were activated by sensations from the limb when it was attached, continue to be activated even though the signals have ceased to come in. It “remembers” the pain — and plays it back like a memory.

Depression is the emotional equivalent of this “learned” pain. The brain gets so familiar with the feeling of misery that it no longer responds to changing circumstances. It is locked into the negative feelings, like a person who is lost in past memories can no longer respond to the changing world. What is needed is to “unlearn” the memory – to nudge the brain back into responding differently, or thinking new thoughts. We will see that this is a physical process. New thoughts occur when new neural pathways are formed between brain cells. If thoughts are repeated these become permanent – like well-trodden paths through a wood. Old pathways slowly disappear if they are not used. “Unlearning” negative thinking therefore involves building new thought pathways and abandoning the old.

It takes time, and practice to establish a whole new pattern of thinking, which remains fragile for a long time. The majority of people who are treated for a first bout of depression relapse within two years of the initial attack. This is often because they abandon treatment as soon as it starts to work, and don’t wait until the new thought patterns are physically well-established. Though drug treatments help, but it is worth noting here that the goal of the first six to eight weeks of antidepressant therapy is symptom relief. Guidelines suggest treatment should continue for at least four to six months to reduce the likelihood of relapse.