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Can opiate painkillers change how you feel about rewards?

Opioids change how we experience rewards, such as winning imaginary money in a game, by affecting brain circuitry in fibromyalgia patients.

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How many times have you hurt yourself badly? How many friends and family members do you know who suffer from sharp pain? In many of these situations doctors will prescribe opioids to numb the pain and prevent the development of bad habits such as avoiding movement. These drugs have gone a long way to make our medical practices more humane as society has grown to take pain more seriously in the past few decades. However medical science has yet to fully understand how opioids affect the brain, whether we’re in pain or not. In the face of a growing opioid epidemic it’s more important now than ever that scientists study how opioids change the circuitry of our brains. 

Opioids fight pain by tapping into the signal relay of neurons of the nervous system that run from the brain down through the spine. This circuit tells other nerve cells to stop sensing pain and gives us relief for a while. Opioids aren’t specific to just pain though. The human body produces opioids to also drive some of our emotions such as endorphins that make us feel good. These feelings of euphoria are a key part of how we learn and interpret the world through what’s known as the reward pathway. For example, when you work out, your body releases dopamine that rewards you with positive feelings and encourages you to continue to exercise your muscles. By adding extra opioids like morphine we start to change the way these pathways work in our brains. This can lead to poor sleep, foggy thinking, and addiction. 

So how should we balance the side effects of taking opioids with the need to minimize pain?

Scientists at Stanford University, CA, have been studying these reward pathways in patients with fibromyalgia, a mysterious condition in which people experience chronic pain for no observable reason. In a recent study, healthy patients, patients with fibromyalgia, and patients who are on an opioid therapy for fibromyalgia, had their brains scanned while playing a game that stimulates the reward pathway. This pathway plays many roles in how we perceive the world and react to experiences such as how strongly we respond to misfortune. In this game, patients were presented with opportunities to gain or lose $5 by pressing a button to accept or reject the offer at a split-second pace. 

While patients played the gain or loss game they laid inside of a Magnetic Resonance Imager (MRI). MRI uses magnetic waves to align a small amount of your atoms, similar to how a magnet will pull iron nails one direction or how the Earth’s magnetic field causes all compasses to point north. As patients play the game blood flow increases to areas of the brain used to process rewards and losses and changes the alignment of atoms in these areas. The MRI machine is able to notice these small changes and creates a picture of brain activity. 

With these scans the researchers were able to look for differences in areas for gain-anticipation (earning money) and in non-losses (avoiding the punishment of losing money) while playing the game. First, people with fibromyalgia who weren’t taking opioids had a weaker response to gaining money but had a stronger response to avoid losing money. This suggests that the chronic pain these patients suffer may be altering the patients expectations. They expect negative results and are quick to avoid punishment. On the other hand, people using opioids to fight fibromyalgia had a very normal response, meaning they were similar to the healthy group. Here the authors explained that this may be due to the positive emotions opioids create. Over a long time of taking these drugs, patients may have developed a more positive outlook that kept them from expecting bad outcomes. Changing the circuitry of the reward pathway may affect things such as relationships and choice making outside of this simple game. 

Though these findings suggest how opioids may change the reward pathway of the brain, the scientists point out that the brain is very complicated. Many experiences can develop different circuits in the brain, possibly making someone naturally more positive or more sensitive to loss. In this way it’s possible the people in this study may have already been different, even before taking opioids. As always, science is a step-by-step process and more research will need to be done to completely understand how opioids affect the brain.

Study Information

Original study: Apparent Effects of Opioid Use on Neuronal Response to Reward in Chronic Pain

Study was published on: 03 July 2019

Study author(s): Katherine T. Martucci, Kelly H. MacNiven, Nicholas Borg, Brian Knutson & Sean C. Mackey

The study was done at: Standford University and Duke University

The study was funded by:

Raw data availability:

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This summary was edited by: Osama Alian