Experiment 2: Reducing Pain in the Brain

A completely different group of researchers, led by Jarred Younger^[1] at the Stanford University School of Medicine used fMRI (functional magnetic resonance imaging) to view the brains of people in an experiment very similar to the one you just studied. Just as in the previous study, they used heat to produce pain, though the location was at the base of the thumb on the palm of the left hand. They used two levels of heat, which they labeled as “moderate” and “high”. They only tested picture-viewing; there was no hand-holding in this study.

Details of the Experiment

Younger and his colleagues tested both females and males by scanning their brains as they looked at pictures of romantic partners or mere friends. There was also a control condition explained below.

Each person brought to the experiment several pictures of their romantic partner. Only participants who reported being “intensely in love” and who scored at a very high level on the Passionate Love Scale (a standardized measure of passionate love) were included in the study. The participants also brought some pictures of a friend or acquaintance of the same gender and attractiveness as the romantic partner. In the experiment, the participants used the same procedures that were used in the other study you read. When looking at the picture, they were asked to focus on the picture and think about the person in the picture (romantic partner or friend).

For a third control or baseline condition, the experimenters wanted to see if looking at the picture was merely a distraction from the pain. In this distraction control condition, the participant was given a category name (e.g., animals, fruits, actors, politicians) and was asked to say aloud as many examples of that category as possible (ANIMALS: dog, bear, salmon, eagle, etc.).

Goal of the Experiment

The experimenters were interested in a very specific hypothesis. They wondered if thinking about someone we love intensely activates our brain’s reward system. This is a group of structures deep in the center of the brain surrounding some neural structures called the basal ganglia (see figure below). Among their reward-related activities is their production of the neurotransmitter dopamine, which they transport to regions throughout the brain. Dopamine is an important part of the pleasure and learning experiences associated with rewarding activities.

Because they were interested in testing the idea that the reward system might be activated by viewing someone we passionately love, the experimenters focused their brain scanning on the reward system areas shown above. However, they also looked at other brain areas, so they could determine if the reward system was more strongly associated with pain reduction than other areas.

Results of the Reward System Experiment

By now, you should have the idea that things are seldom simple in the world of science. First, the basic results from the first study you read about were found here as well. Participants reported significantly less pain when they looked at a picture of their romantic partner than when they looked at a stranger. Unfortunately (if you wanted simple results), almost exactly the same reduction in pain was found in the distraction control condition. The figure below shows the results. These researchers used an 11-point pain scale (0=no pain, 10=worst pain imaginable), so the numbers cannot be directly compared to those in the first study. However, higher numbers mean more pain, so you can easily interpret the results.

 

These results alone suggest that looking at pictures of someone we love may be nothing more than a distraction from the pain. However, this experiment was different than the first one because it had another dimension: the brain scans. What did they indicate?

Brain Imaging Results

The brain images add an interesting dimension to our understanding of pain and pain relief. When participants were looking at pictures of their romantic partner, the reward regions of the brain were very active. In fact, there was a strong correlation between the amount of activity in this region and the level of pain the person reported: more activity was associated with less pain.

If the reward systems (in the figure above, the red circle in the brain on the left) were also activated by the distraction task, then we are back to the idea that looking at our romantic partner is just a way of distracting ourselves. But that is NOT what they found. Activity in the reward regions of the brain were not strongly correlated with pain relief during the distraction task. However, other regions of the brain did have a strong relationship to pain relief in the distraction condition (see the blue circles on the brain to the right in the figure above). These are brain areas involved in memory, language, and making choices—exactly the systems that are active when we think about words that fit a particular category.

Conclusions

This study by Jarred Younger and his colleagues suggests that there may be multiple ways to reduce our experience of pain. The two approaches studied here (touching someone we love in Experiment 1 and generating words in Experiment 2) may produce similar analgesic effects: both result in less pain. But in terms of underlying causal mechanisms, such as the brain systems involved in reducing pain, very different things may be taking place.

This is not the end of the story. Finding a brain region associated with some experience is not an explanation; it is simply a first step in finding how a brain system works. Finding two sets of brain regions that both produce the same effect suggests that our explanation of how pain reduction is accomplished by the brain is not going to be simple.

Finally, if you were hoping to find out if there were sex differences in the effects we discussed, unfortunately, the experimenters felt they did not have enough subjects to reliably test to see if men and women differ in their response to pain or in the regions of the brain associated with pain reduction. Perhaps one of you will conduct the experiment that answers those questions!

General Conclusions

We started this exercise with a discussion of social support and health. People with stronger social support networks tend to have better health outcomes. When we asked how this works, we zoomed in on a very specific type of social support: a romantic relationship, which involves deep and complex connections between two people. It would be reasonable to suggest that this type of relationship might have the potential to produce the strongest possible form of social support.

Both experiments showed that social support in the form of touching someone we love (or seeing a picture of that person in the first experiment) can reduce pain, when compared to control conditions. The second experiment points to the brain’s reward system as a possible source of pain relief. We still don’t know the brain mechanism that produces the pain experience; it is possible that we fully feel the pain, but the positive feelings associated with the person we love balance out the negative experience of pain. Or perhaps the reward system can actually turn down the intensity of the pain experience, so we really feel less pain when we are with those we love. The scientists of your generation will have the opportunity to explore these mysteries.

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