It's well established that chronic pain afflicts people with more than just pain.
With the pain come fatigue and sleeplessness, depression and frustration, and a noticeable disinterest in so many of the activities that used to fill a day.
It makes sense that chronic pain would leave patients feeling weary and unmotivated - most people wouldn't want to go to work or shop or even meet friends when they're exhausted and in pain.
But experts in pain and neurology say the connection between chronic pain and a lousy mood may be biochemical, something more complicated than a dour mood brought on from persistent, long-term discomfort alone.
There is now evidence that chronic pain triggers a series of molecular changes in the brain that may sap patients' motivation.
Hopefully this study will lead to new treatments for the behavior changes that come with chronic pain. The new research improves understanding of the biochemical effects of chronic pain and may be a comfort to patients who blame themselves for their lack of motivation.
Chronic pain is more than simply pain that lasts for a long time. Perhaps the easiest definition is pain that persists after the initial injury or illness that caused it - pain that has stayed longer than it should have or that serves no useful purpose.
Roughly 100 million Americans suffer some kind of chronic pain. The source of chronic pain varies widely - it could be back pain, migraines or arthritis. Cancer can cause chronic pain long after treatment is complete.
Some patients have conditions entirely defined by pain, such as fibromyalgia, which causes widespread muscle pain, or neuropathy, which can feel like a burning, tingling pain in the hands, feet or other part of the body.
Chronic pain is not just prolonged acute pain. There are changes that define the chronic pain condition.
Both chronic and acute pain can affect a person's level of motivation, and the biological mechanism for that behavior change may be similar in both types of pain. But with acute pain, the reason for the motivation loss is beneficial. With chronic pain, it's not.
Many pain experts believe that when pain turns chronic, the same biochemical changes happen that happen with acute pain, but they're no longer useful. Patients with arthritis, for example, may be physically able to pursue an active lifestyle, and even benefit from it, but changes in their brain may leave them completely lacking in motivation.
Not a mental flaw
Short of a drug for specific emotional and mental problems caused by pain, pain clinics treat chronic conditions.
The treatments go far beyond providing pain killers. For many patients, dealing with the effects on their mood is more important to their quality of life than treating the pain itself.
The new research and others like it may not offer new treatments or provide the full answer as to what's happening in the brain during pain. But some patients might find it reassuring to know that it's a biochemical change that's sapping their motivation, and not some mental or emotional shortcoming.