When it hurts so bad, why does my brain light up?

If you’ve ever been rejected by a loved one, you knows that it hurts. Think of the language that we use to describe the feeling – hurt, pain, broken hearts, heartache, and so on. Across cultures, many of the same words are used to describe social rejection and bodily pain. Is this all just metaphor, or are people who have been dumped genuinely feeling physical pain? A recent study by Ethan Kross and colleagues set out to address this question by putting volunteers who had recently experienced such intense rejection into brain imaging machines.

The principle behind brain imaging is straightforward. As you start taxing your brain, different neural circuits are called into action. These brain regions need to consume more oxygen, which is provided through the blood supply. Oxygen travels in your blood by binding to the iron that is present. This changes its magnetic properties in a way that an MRI machine can detect. The machine tracks where all the oxygen-carrying blood is going, and the places that ‘light up’ with oxygen are the brain regions being used the most.

The researchers recruited people who felt intensely rejected as a result of being dumped (an “unwanted romantic relationship break-up”) sometime in the last 6 months. The subjects were asked to perform two sets of tasks while in the brain scanner.

Experiment 1. The subjects would look at a photo of their ex partner, and think specifically about their experience of being rejected. They would then look at a photo of a friend of the same gender as their ex-partner, and think about a recent positive experience they shared with them. The experimenters compared the brain scans from the two experiences and identified regions that respond more heavily to the ex-partner than the friend. Their claim is that the regions thus identified are involved in processing social rejection.

Experiment 2. In one trial the subjects would be made to feel uncomfortably hot on their forearm. In the other, they were exposed to a stimulus that was warm, but not painfully hot. The researchers compared their measurements from these two tasks to identify brain regions that respond more intensely to the sensation of heat than to warmth. These should include regions involved in processing pain.

It turns out that there were regions that lit up in both the social rejection and physical pain experiments. These common regions fell in two different functional categories- let’s call them the Oh and the Ouch. The former are areas involved with sensing painful stimulus, whereas the latter are regions involved with the actual unpleasant feeling of pain. The researchers then looked up these specific brain regions in the literature, in over 500 studies. They found that the majority of these studies showed that indeed these regions were activating in response to physical pain. In other words, love hurts, and it can hurt in just the same way that physical pain does.

The discovery that an intense emotional experience can share a brain region with a visceral physical experience harks back to an old theory of emotion. According to this idea, our emotions arise in response to physiological changes in our body. When you get angry, you are actually responding to the sensation of your pulse racing, your muscles tightening, your adrenalin surging, and other cues from your body. This is the James-Lange theory of emotion put forward in the 19th century, and it has since fallen into disuse. But its modern embodiment (sorry) is the idea that our emotions are strongly modulated by the feedback that we get from our body, and it has been gaining experimental support. There’s a fascinating Radiolab episode that discusses the implications of this idea.

This study raises the following question to my mind: if there are people who experience physical pain with less intensity than the rest of us, are they similarly blunted to the feeling of being rejected? The 19th century ideas of William James and others may still be quite relevant to our modern understanding of emotion.

Image Reference The header image is a screenshot from a wonderful short film by Will Hoffman and Daniel Mercadante, created for Radiolab’s episode on Words. You can watch it here.

References

Kross E, Berman MG, Mischel W, Smith EE, & Wager TD (2011). Social rejection shares somatosensory representations with physical pain. Proceedings of the National Academy of Sciences of the United States of America, 108 (15), 6270-5 PMID: 21444827 Link

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8 Comments

Filed under Biology

8 responses to “When it hurts so bad, why does my brain light up?

  1. deturing

    One, I’m guessing this generalizes, so that all emotional pain/trauma should activate these regions. It’s very interesting though cos it doesn’t stem from a standard sensory input. It seems like some feedback loop within the brain – I don’t even know how to think about it 🙂

    Two, regarding the questions you’ve raised, a priori I don’t necessarily see a connection. e.g., if someone has suffered damage to “sensors” on skin, he/she will probably not feel pain as much, or someone with huge muscles will probably take better to a sprain etc (though it’s not clear how we’re measuring induced pain here). Anyway, the emotional pain seems to emerge wholly within the brain and is not really triggered by physical senses, so it’s not at all obvious how or if at all they are related.

    Three, if I may make a gross generalization, it might be that it’s a good feeling/bad feeling divide. e.g., do the same regions activate when someone yells at you? What is chemically known about these brain regions? Also how is all this related to dopamine/serotonin levels etc.? (I know, I can look it up, but lazy :P)

    • Aatish

      Hey Deepak. You raise some pretty good points. Let me address them in reverse.

      3. I looked it up (you knew I would ;)) and apparently dopamine sensitive neurons are mainly located in the frontal cortex, whereas the regions that activate in this study are in a different region called the operculum insula. Of the 500+ studies in which this region lit up, 75-88% (depending on which specific region) of them were studies about pain stimulus. And I would imagine there would be many studies on depression and dopamine that didn’t light up this region, suggesting that this is pain related and not just in response to more general bad feelings.

      2. You’re right, if the problem was in your pain receptors, then it shouldn’t affect emotional pain. Though it still could, if say the reduced sensitivity of these receptors meant poorer development of the pain sensitive region of your brain. I was thinking more along these lines: if there was a problem with the brain region that detects physical pain, this study implies that it should also affect sensitivity to emotional pain. I think the radiolab episode vaguely mentions some studies where people who became paraplegics reported a kind of emotional numbness as well. It would be interesting to follow that up.

      1. Related to sensory input, one thing that didn’t make sense to me in the paper is why the response to physical pain wasn’t more asymmetrical. They applied pain to the left forearm, I would imagine this would have lead to a stronger pain response in right brain than left (since that’s where the sensory input is coming to). Don’t quite get it.

      • deturing

        Ya know, what if the response from pain that’s registered in this (operculum insula) region of the brain is a secondary response, and is actually the same “feeling” as a break up (or having a reasonable overlap). We may not be able to distinguish it, also probably because it’s fleeting, but if that’s the case, then the whole result is kind of moot. I think it is important to note the other regions of the brain that activate too. This is obviously not the ONLY active region for pain.

  2. Erik

    Excellent new blog. I think you ask an interesting question:

    “This study raises the following question to my mind: if there are people who experience physical pain with less intensity than the rest of us, are they similarly blunted to the feeling of being rejected?”

    This question, however, seems (somewhat) outside of the scope of brain imaging studies. That is, while these studies are interesting to understand which areas of the brain are affected the more seminal question is how people conceptualize pain in the first place. This leads us back to the black box which neuroscience leaves unaddressed.

    • Aatish

      Thanks, Erik.

      Admittedly, addressing the conscious experience of physical sensations is THE biggest problem in neuroscience. But I don’t think you need to go there. You could measure, say, the physiological consequences (pulse rate, sweating, chemical responses) in people exposed to a certain threshold of pain. Or you could adopt a more subjective approach and have people rate their level of pain to a stimulus on some sort of standardized scale.

  3. Su Bose

    How to measure pain thresh-hold? That would indeed be an interesting and important area to start exploring .. because Aatish questions like that play in my head too in trying to understand people’s varying response to ‘similar’ stimuli. Some jump back easily .. some carry scars all their lives unable to forget.

    Are we trapped by our chemicals and neural circuitry [as well as our DNA] unknowingly ‘feeling’ these rejections / pains in different degrees?

    If we knew more about it .. would we try to “tweak” our chemistry?

    Does it affect our ability to empathize with our fellow beings? Those who feel more intensely than others also resonating with other being’s rejection / sorrow / loss than those who feel such things at a more ‘shallow’ level.

    There was once a study done on “thrill seekers” those who can undertake derring do stuff that normal humans never dream of doing .. because they have a very HIGH Thresh hold for activating their adrenaline response – fear .. pulse high .. feeling sick to the pit .. and general excitement from the ensuing feel good hormone release .. I am using extremely lay language here .. It could be the same way for all these other feelings too.

    Oh and let’s not forget the famous PMS story :-)) Yes that is proven .. chemical changes in the body of a woman during certain times of the month does affect decision making to some extent and general well-being and optimism .. and in different women in different degrees.

    Basically it IS IMPORTANT to start looking at ways to try to quantify such ‘lighting up’ with standard stimuli .. Even tho foreseeably it will open a Pandora’s Box

    cheers
    quick thoughts from Suj

    • Aatish

      Hi Suj. Thanks for your comments, a lot of interesting thoughts packed in there. Re: being trapped by our chemicals, in many cases we are already eroding these contraints by tweaking our brain chemistry to control depression and some neurological disorders. It must be the case that our brain chemistry, and perhaps genetics plays a large role in how we interact with others, and this is a somewhat alarming thought. But, by understanding these processes better, we can begin to make changes in the directions that we want to go

      I think you’ll find this story interesting. It’s about a mutation that supposedly affects how empathetic people here, and how sensitive they would be as parents. Turns out that culture can play a big role in determining these effects.

  4. Erik

    Thanks for your response. I appreciate your creative thinking in forming proxies for how to “objectively” measure different responses to pain. I don’t think this gets one any closer to the elusive “black box”, but probably can help one figure out the contours of what the box may ultimately look like.