How We Experience Pain of Others

Definition

Pain

Chronic pain is classified as pain that lasts longer than three to six months. In medicine, the distinction between acute and chronic pain is sometimes determined by the amount of time since onset. Two commonly used markers are pain that continues at three months and six months since the beginning. Chronic pain may originate in the body or brain, or spinal cord. It is often difficult to treat. Epidemiological studies have found that 8 to 11.2% of people in various countries have widespread chronic pain. Chronic pain is one of the most costly health problems in the U.S. Increased medical expenses, lost income, lost productivity, compensation payments, and legal charges are some of the economic consequences of chronic pain. Pain Scale Chart: 1 to 10 Levels: Pain scale diagram and chart that includes an explanation of each of the one to ten classified pain levels.

Main Digest

A new study from the Netherlands Institute for Neuroscience recorded from neurons of human patients to show that the pain of others is directly mapped onto neurons in the insula - a brain region critical for our emotions.

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Sharing the distress of others is considered key to empathy and our motivation to help others. With people greatly differing in their ability to empathize and some psychiatric patients lacking the ability to empathize, understanding how our brain makes the pain of others feel painful is key to understanding the origin of these individual differences.

So far, we have had to rely on fMRI studies to identify brain regions that become activated while we perceive the pain of others. Unfortunately, fMRI cannot directly measure the activity of neurons. Instead, it measures changes in blood flow that help pinpoint brain regions associated with empathy. To understand where in the brain neurons help us share the distress of others, we would need to insert electrodes into the brain and directly measure the electrical activity through which neurons process information. For obvious reasons, this is impossible in humans, or is it?

Epilepsy Patients

In certain cases of epilepsy that cannot be treated using pharmacological treatments, surgeons implant electrodes directly into the brain of patients to localize the origin of epilepsy. The patients then have to stay in the hospital for about a week while the surgical team records their brain activity and waits for an epileptic event to occur. To add purpose to this waiting, some patients volunteer a unique opportunity to understand the human mind better: they engage in psychological tasks while their brain activity is measured through these medical electrodes.

In a new paper published in the prestigious journal eLife, a collaboration between NIN researchers Efe Soyman, Rune Bruls, Kalliopi Ioumpa under the supervision of professors Christian Keysers and Valeria Gazzola leveraged this unique opportunity to test the notion that neurons in brain regions involved in our pain, like the insula, contain neurons with an activity that directly mirrors the pain of others. They showed patients short video clips of a woman experiencing various pain levels. They measured how strongly neurons in the insula - a brain region involved in the patient's own pain experiences - respond to the pain they observed the woman in the video clip experience. Specifically, they could measure intracranial local field potentials, which measure the activity of some hundreds of insula neurons close to the electrode, from 7epilepsy patients. In addition, they could zoom into the activity of individual neurons in the insula of 3 epilepsy patients.

Background: The insula and our own emotions

The insula, a brain region hidden inside the brain, plays a critical role in our emotions. It can sense the state of our body through input from our inner organs and skin, integrates this information with what we see, hear and smell, and is thought to give rise to these conscious feelings we call emotions. In particular, it has also been shown to contain many neurons that respond when we experience pain in or on our own body, with the level of its activity scaling with how unpleasant we find this pain.

The novelty: coding the pain of others

The team, therefore, explored whether neurons in this region would also represent the level of pain experienced by others. Because the movies they showed participants varied in how much pain the actress in the movies was experiencing, the team could explore whether movies in which the patient's perceived others to be in more pain would be movies in which the insular neurons would show more activity - serving as a mirror for other people's pain. This is exactly what they found: throughout the insula, they could record electrical activity that scaled with the pain the people reported perceiving in the movies. This was true in the local field potentials and individual neurons, providing the first evidence that a brain region involved in our pain contains a fine-grained representation of how much pain others experience.

Using advanced data analysis methods, the team could take the level of electrical activity in the insula during each movie and predict how the patient would respond to the question: "how intense do you think the pain was that the person in the movie experienced." By offering the unique opportunity to record from their brain directly, the patients thus provided us with a key insight into human empathy: it looks as though we empathize with the pain of others because our brains are wired to transform their pain into activity in regions involved in our pain.

How do we perceive the pain of others?

The team provided further insights into how we perceive the pain of others. In half the videos, the camera was focused on the facial expression of the actress, which was seen to unfold from a neutral expression to one of varying degrees of pain in about one second. Analyzing the electrical responses in the insula and the muscle movements of the actress in the movies revealed that what the brain appears to use to perceive the pain of others was not the movement per se, but how contracted the eyes of the actress ended up being. In the other half, the camera focused on the actress's hand and showed a belt hitting the hand. In that case, the brain appeared to deduce the amount of pain from processing how much the hand was moving under the action of the belt. Together, this revealed intricate details of how flexibly the human brain transforms what we see others do into a fine-grained perception of their inner states.

While this study focused on a single brain region, the insula, that fMRI studies had suggested being important for empathy, future team research will aim to combine the data from all recorded electrodes. They can then develop a map of where in the brain the pain of others is transformed into the nuanced empathy we can have for other people's emotions and pinpoint the locations in which differences across individuals could account for the striking differences in empathy we can observe around us.

Christian Keysers:

"As a neuroscientist, our dream is to understand how neurons make us who we are. What these patients do, by allowing us to record from these electrodes, is to make that dream come true: we could see, in real-time, how the pain of someone else is mirrored in the neurons of an observer. After decades of working on empathy, we could see empathy unfold in the human insula".

Efe Soyman:

"Other people's suffering can be inferred from a variety of indicators: a painful expression, the intensity of the event that inflicts pain in them, etc. With this precious data we collected from the patients, we see how the human insula might tune into whatever is available among these various cues when we experience other people's pain."

Acknowledgements:

This work was made possible through a tight collaboration between the members of the social brain lab that designed the tasks and analyzed the data (Efe Soyman, Rune Bruls, Kalliopi Ioumpa, Laura Müller-Pinzler, Selene Gallo, Chaoyi Qin, Christian Keysers and Valeria Gazzola), clinicians at the VUmc in Amsterdam that performed the surgeries and helped in data acquisition (Elisabeth CW van Straaten, Johannes C Baayen, Sander Idema), and the team of Prof. Pieter Roelfsema and Matt Self (Matthew W Self, Judith C Peters, Jessy K Possel) that have established the link between the fundamental research at the NIN and the clinicians at the VUmc, and also helped acquire the data. We extend our warmhearted gratitude to the patients who participate, making these scientific insights possible.

Attribution/Source(s):

This peer reviewed article relating to our Pain: Acute and Chronic section was selected for publishing by the editors of Disabled World due to its likely interest to our disability community readers. Though the content may have been edited for style, clarity, or length, the article "How We Experience Pain of Others" was originally written by Netherlands Institute for Neuroscience (KNAW), and published by Disabled-World.com on 2022-11-12 (Updated: 2023-01-04). Should you require further information or clarification, Netherlands Institute for Neuroscience (KNAW) can be contacted at herseninstituut.nl. Disabled World makes no warranties or representations in connection therewith.

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