eLife: How do we feel the pain of others?

A new study from the Netherlands Institute for Neuroscience documents neurons in human patients, showing that the pain of others is mapped directly to neurons in the insulus, an area
of the brain that is vital to our own emotions.

Sharing the pain of others is considered key
to generating empathy and motivation to help others.
Since people's capacity for empathy varies widely, and some psychopaths lack the ability to empathize, understanding how our brains make others miserable is key to
understanding the origins of these individual differences.

Until now, we have only relied on fMRI studies to determine which areas of the brain are activated
when we perceive pain in others.
Unfortunately, fMRI cannot directly measure the activity of
neurons.
Instead, it measures changes in blood flow, which helps pinpoint brain regions
associated with empathy.
To understand which parts of the brain neurons help us share the pain of others, we need to insert electrodes in the brain that directly measure the electrical activity
of neurons as they process information.
Obviously, this is impossible in humans, is it?

epileptic

In some cases of epilepsy that cannot be treated with drugs, surgeons implant electrodes directly into the patient's brain to locate the origin
of the epilepsy.
Patients must then stay in the hospital for a week or so, while the surgical team records their brain activity and waits for the epileptic event to occur
.
For the purpose of increasing this waiting, some patients volunteered to provide a unique opportunity to better understand the human mind: when they performed mental tasks, their brain activity was measured
through these medical electrodes.

In a new paper published in the prestigious journal eLife, NIN researchers Efe Soyman, Rune Bruce and Cariopi Yumpa, under the supervision of Professors Christian Kaisers and Valeria Gazzola, took advantage of this unique opportunity to test the concept that neurons in areas of the brain related to our own pain, such as the insulas, contain active neurons
that directly reflect the pain of others 。 They showed patients a short video of women experiencing varying degrees of pain and measured the intensity of how strongly
neurons in the insula (brain regions associated with the patient's own pain experience) responded to the pain experienced by the women in the video.
Specifically, they were able to measure intracranial local field potentials from seven people with epilepsy, measuring the activity of
hundreds of insula neurons near the electrodes.
In addition, they were able to amplify the activity of
individual neurons in the insula of 3 epilepsy patients.

Background: Insula and our own emotions

Insula is a brain region hidden inside the brain that is known to play a vital role
in our emotions.
It can sense the state of our body through input from our internal organs and skin, and combine this information with our sense of sight, hearing, and smell, which is thought to produce these conscious feelings
known as emotions.
In particular, it has also been shown to contain many neurons that respond when we experience pain in ourselves or on our bodies, and its level of activity is proportional to
how unpleasant we are with this pain.

The novelty: coding the pain of others

So the team explored whether neurons in this region also represent the level
of pain experience of others.
Because the movie they showed participants was different from the level of pain experienced by the actresses in the movie, the team could explore whether insular neurons showed more activity in movies where patients felt more pain from others—acting as a mirror of
other people's pain.
That's exactly what they found: Across the insula, they could record electrical activity
corresponding to the pain people felt in the movie.
This is true in local field potentials, even in individual neurons, which provides the first evidence that brain regions associated with our own pain contain precise representations
of the level of pain experienced by others.

Using advanced data analysis methods, the team was able to measure the level of electrical activity in the insula in each movie and predict how patients would respond to the question: "How intense do you think the pain experienced by the person in the movie is?" By providing the unique opportunity to record directly from their brains, these patients provide us with a key insight into human empathy: We seem to truly empathize with the pain of others as our brains connect to transform their suffering into activity
in areas related to our own suffering.

How do we perceive the pain of others?

The team provides further insights
into how we perceive the suffering of others.
In half of the video, the camera focuses on the actress's facial expressions, and it can be seen that in about a second, the actresses' facial expressions change from neutral expressions to varying degrees of pain
.
Analysis of the electrical response and muscle movements of the actress's insula in the film revealed that it seems that what the brain uses to sense the pain of others is not the movement itself, but how far
the actress's eyes eventually contract.
In the other half of the shot, the shot focuses on the actress's hand and shows a belt hitting her hand
.
In this case, the brain seems to infer the degree of
pain by processing how much the hand moves under the action of the belt.
Together, this reveals how the human brain flexibly translates the actions we see of others into intricate details of their inner state
.

While the study focused on a single brain region, the insula, which fMRI studies have shown is important for empathy, the team's future research will aim to combine all recorded electrode data
.
They can then draw a map of where in the brain the suffering of others is translated into subtle empathy for the emotions of others, and pinpoint where differences between individuals can explain the significant differences
in surrounding empathy we observe.
The link between intensity