Memory Problems and Chronic Pain

Half jokingly, patients with chronic pain can sometimes start to wonder whether they are coming down with Alzheimer’s. They don’t seem to remember anything anymore. Besides memory problems, it can be hard to concentrate, multi-task, and find the right word to use – that experience when the word you want to use is “on the tip of your tongue.” People with fibromyalgia have even given these problems a nickname – “fibro fog” – as in when your head is in the clouds.

More professionally, we might call these problems “mild cognitive problems” or “mild cognitive deficits.” The term “cognitive,” of course, comes from the noun “cognition,” which is a catchall term for types of thinking, such as concentration, memory, multi-tasking, use of language, etc. The use of the term “mild” is not meant to minimize the extent of these problems, as patients can report them to be quite problematic. Rather, the use of the term is common among healthcare providers because it contrasts the extent of these problems with people who typically have more severe cognitive deficits, such as those with traumatic brain injuries or dementia.

So are the memory problems that seem to go along with chronic pain real? What’s the connection between chronic pain and memory problems?

Is the connection real?

Over the years, healthcare providers have asked themselves this question and scientists have put it to the test. There’s a couple of ways of going about doing it. It takes a little bit of explaining first.

One way researchers determine whether the reports of memory problems are real is to use psychological tests of memory. They test a large group of patients with chronic pain and they test a large group of people without chronic pain. Next, they compare the average scores of both groups. If the average score of the chronic pain group is significantly different (and worse) then the average score of the group without chronic pain, then they conclude that the memory problems of the chronic pain patients are real.

Another way researchers can determine whether the memory problems of chronic pain patients are real is to take studies like those described above and combine them into one super large study. They find the studies published in professional journals. They do a systematic search for all such studies and then combine them. This type of study is called “a meta-analysis.” Meta-analyses are thought to be the most valid kind of study because it combines many studies, any one of which in isolation may have produced erroneous results. In other words, in science, large studies are better, because any potential errors that can occur along the way get watered down by the large number of studies and don’t throw off the main results.

A meta-analysis on the relationship between memory problems and chronic pain is what Berryman, et al. (2013), published in this month’s issue of Pain, a leading professional journal in the field of pain management. They combined 24 studies that tested the memory abilities of people with chronic pain and compared them to the memory abilities of people without chronic pain. They found a consistent, moderate deficit in what’s called ‘working memory’ for people with chronic pain.

Working memory is the ability to hold information in mind in order to do something. It involves short-term memory, attention, and information processing. You use working memory when deciding upon doing something and setting out to do it, such as when you decide to get something from the basement. You have to hold the thing in mind while walking down into the basement and remember what it is you are looking for when you get there. You use working memory when learning to do something. You have to hold the instructions in mind while you practice it. You also use working memory when multi-tasking. You have to hold information in mind while engaging in the different activities.

In sum, Berryman, et al., (2013) found that people with chronic pain had moderately lower scores on tests of working memory when compared to the scores of people without chronic pain on the same tests. This finding is consistent with the common complaints of memory problems by chronic pain patients.

What is the connection between chronic pain and memory problems?

To understand the connection between chronic pain and memory problems or other forms of cognitive problems, we have to review a known fact that is commonly overlooked. This fact is that the experience of pain occurs because of our brain and other parts of our nervous system. Whatever the initial cause of pain, once pain becomes chronic, it becomes a nervous system problem. Different areas of the nervous system, such as in the brain and spinal cord, go through changes and these changes are responsible for the development of chronic pain.

One area of the brain that appears to go through such changes is the hippocampus (Cardoso-Cruz, Lima, & Galhardo, 2013; Mutso, et al., 2013). The hippocampus is involved in the development of central sensitization (Lamtremoliere & Woolf, 2009), depression (Campbell & MacQueen, 2004), and memory (Squire, 1992). Pain can change the hippocampus. In turn, these changes to the hippocampus can create a cascading effect on the experience of pain, leading to central sensitization, depression, and memory problems.

Much is yet to be learned from the study of chronic pain and the nervous system. The hippocampus may not be only thing that is responsible for the development of memory problems in people with chronic pain. Indeed, in all likelihood, it is not the only thing that leads to such problems. At the very least, though, it is likely a part of the connection between chronic pain and memory problems.

References

Berryman, C., Stanton, T. R., Bowering, K. J., Tabor, A., McFarlan, A., Mosely, G. L. (2013). Evidence for working memory deficits in chronic pain: A systematic review and meta-analysis. Pain, 154, 8, 1181-1196.

Campbell, S. & MacQueen, G. (2004). The role of the hippocampus in the pathophysiology of major depression. Journal of Psychiatry & Neuroscience, 29, 6, 417-428.

Cardoso-Cruz, H., Lima, D., & Galhardo, V. (2013). Impaired spatial memory performance in a rat model of neuropathic pain associated with reduced hippocampus-prefrontal cortex connectivity. Journal of Neuroscience, 33, 6, 2465-2480.

Lamtremoliere, A. & Woolf, C. J. (2009). Central sensitization: A generator of pain hypersensitivity by central neural plasticity. Journal of Pain, 10, 9, 895-926.

Mutso, A. A., Radzicki, D., Baliki, M. N., Huang, L., Banisadr, G., Centeno. M. V., Radulovic, J., Martina, M., Miller, R. J., & Apkarian, A. V. (2012). Abnormalities in hippocampal functioning with persistent pain. Journal of Neuroscience, 32, 17, 5747-5766.

Squire, L. R. (1992). Memory and the hippocampus: A synthesis from findings with rats, monkeys, and humans. Psychological Review, 99, 2, 195-231.

Date of last modification: 8-12-2013

Author: Murray J. McAllister, PsyD

About the author: Dr. McAllister is the executive director and founder of the Institute for Chronic Pain (ICP). The ICP is an educational and public policy think tank. Our mission is to lead the field in making pain management more empirically supported. Additionally, the ICP provides scientifically accurate information on chronic pain that is approachable to patients and their families. Dr. McAllister is also the clinical director of pain services for Courage Kenny Rehabilitation Institute (CKRI), part of Allina Health, in Minneapolis, MN. Among other services, CKRI provides chronic pain rehabilitation services on a residential and outpatient basis.