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Pain Brings Out Our Mean Streak

Physical pain can make us more aggressive.

Key points

  • A recent study among college students induced pain and aggression simultaneously to explore the relationship.
  • The researchers conducted fMRI scans of brain regions associated with social information processing.
  • Pain was shown to reduce activity in regions involved with processing social information and directing appropriate responses.
Engin Akyurt/Pixabay
Source: Engin Akyurt/Pixabay

When I was 10 years old, some college friends of my parents visited our home with their two sons, one nine and the other 11. Upon arrival, the couple announced that their older son was suffering from an abscessed tooth and as a result was feeling “grumpy.”

True to his parents’ word, Mark (let’s call him) was grumpy all morning. It remained nothing more than a low-level, mildly unpleasant sort of grumpiness, however, until just after lunch, when he discovered my BB gun in the closet and promptly barricaded himself in our backyard, forbidding the rest of us kids to enter the trellis gate under threat of injury by copper pellet.

A stern talking-to from his father disarmed Mark before anyone lost an eye, but the incident raised an interesting question. How could a toothache turn an ordinarily sociable, fun-loving (by his parents’ account) child into a pellet gun-wielding desperado? An article recently published in Social Cognitive and Affective Neuroscience offers some possible answers to the question.

Pain can increase aggressive behavior.

Previous research has shown that physical pain can increase aggressive behavior. A team of researchers from China conducted a study to find out why, using functional magnetic resonance imaging (fMRI) scanning to “investigate the neural mechanisms underlying pain-induced aggression.” Fifty-nine student participants were divided into two groups: a pain condition and a control condition. To participants in the pain condition, a cream containing capsaicin—a chemical irritant commonly found in chili peppers—was applied on the volar side of their dominant forearm. Participants in the control condition had a hand cream applied to the same area.

To induce aggression in the participants, a “social network aggression task” was administered in two stages. In the first stage—conducted a week before fMRI scanning—participants were asked to fill out a resume and upload a photo of themselves, and then were presented with resumes and photos of 30 other college students, which they were instructed to evaluate with either positive, negative, or neutral feedback (i.e., “I like your resume,” “I don’t like your resume,” “I neither like nor dislike your resume”). Even though their resumes and photos were not actually being judged, and the photos with which they were presented were stock photos taken from an existing database, participants were told that their resumes and photos were being evaluated by other college students with the same criteria they had used in their own evaluations.

In the second stage, which took place in the laboratory, participants had the cream (capsaicin or hand cream) applied to their forearm and underwent fMRI scanning while supposedly receiving feedback on their resumes and photos from the 30 students they had been told would review them. After receiving the feedback, participants were given the opportunity to administer an electric shock to the person they believed was responsible for the review.

In keeping with human nature in general, behavioral results revealed that both the pain and the control groups showed more aggression in response to negative feedback than they did toward positive or neutral feedback. The pain group, however, responded even more aggressively to negative feedback than the control group did. Significantly, they also responded more aggressively to neutral and even positive feedback than the control group did, suggesting that pain increased aggression regardless of feedback type.

Brain scans revealed interactions between pain and social feedback.

The fMRI scans taken during the task revealed interesting interactions between feedback and pain in regions of the brain involved in “social information processing.” During the feedback processing phase, the control group responded to both negative and positive (as opposed to neutral) feedback with increased activation in the right insula, the anterior cingulate cortex, and the left orbitofrontal cortex.

A core node of the salience network, the insula is believed to detect salient stimuli and “initiate appropriate control signals.” The orbitofrontal cortex, considered a key part of the valuation system, has been shown to play a role in “encoding information values and guiding decisions.” The anterior cingulate cortex is a part of the salience network that “is specialized in processing negative affect, pain, and cognitive control.” In response to socially significant information (i.e., negative and positive feedback), brain activity in the control group increased in brain regions involved in evaluating the significance of social information and responding appropriately to it.

Pain reduced the brain's ability to process social information.

Among participants in the pain group, however, these same regions showed no such increase in activity in response to negative and positive feedback. The response to socially significant information that was shown in these brain regions among the control group “was eliminated by physical pain,” suggesting that the parts of the brain that are typically involved in representing and processing social information were so occupied with processing the unpleasantness of the pain that they were unable to “allocate sufficient cognitive resources to other salient stimuli in the environment" (i.e., the positive and negative feedback from the resumes). In other words, pain reduces our brain’s ability to determine and execute appropriate responses in our interactions with other people.

Whether the source is an abscessed tooth or a chemical irritant on our skin, physical pain can cause us to lash out at the people around us in response to perceived provocations that our normal nonsuffering selves would take in stride as part of the give-and-take of ordinary social interaction.

And while this finding does not exactly excuse barricading oneself in the backyard with a BB gun, any more than it excuses giving someone an electrical shock because of a negative critique of one’s resume, it does go a long way toward explaining such curiously irrational behaviors. It also serves as something of a warning about how to behave around a friend or colleague who leads a conversation by informing you that they have a really bad headache, or—perish the thought—an abscessed tooth.


Yanfang Wang, Lu Li, Junhao Cai, Huaifang Li, Chenbo Wang, Incidental physical pain reduces brain activities associated with affective social feedback and increases aggression, Social Cognitive and Affective Neuroscience, 2022;, nsac048,

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