It’s easy to imagine people with persistent pain have cause to become depressed. After all, it’s a problem that affects every part of life, not just the bit that got injured.
But like so much to do with persistent pain, it becomes harder to unravel exactly what the relationship is when one digs a little further. For instance, it has been repeatedly shown that people with increased emotional distress going in to surgery use more painkillers and generally fare worse afterwards.
On the other hand, we have also known for a long time that unexplained pain is one of the common features of diagnosable depressive illness.
Which comes first?
The complicated answer is the relationship goes both ways. Having already had depression or anxiety increases the risk of developing persistent pain, but if you develop a chronically painful condition without such a history, you have dramatically increased chances of being diagnosed with depression not many months later.
No two central nervous systems are exactly alike. In the case of vulnerability to both depression and pain, this is important. The term allostatic load is applied to what Hamlet called the “slings and arrows of outrageous fortune”. The more severe the episodes of stress or adversity you have had to face, the more your nervous system adapts to reflect these experiences.
Watch: The difference between depression and sadness, explained. (Post continues after video.)
It so happens that many of these changes occur to brain regions that process bodily pain, mood, sleep, anxiety and motivation. These structures are collectively called the limbic system and are thought to have evolved very soon after mammals split from reptiles.