Empathy and Pain in the Evolution of our Social Brains
My first mouse of the day was called “LG1202”. Had I met this mouse in a different time, maybe found him in a pet store or in my back yard, this wouldn’t have been the name I’d chosen for him. To me, he was more of a “Peanut” or “Potato”, something to match his compact, doughy little body and his big wet inquisitive eyes. He didn’t look like an “LG1202”. No one really looks like an “LG1202,” though, and there’s strategy in this. When we work with animals, we name them in a utilitarian way, a numerical shorthand to organize the dozens or hundreds of animals we might work with during our tenure in the lab. These designations might have their own internal logic, maybe referring to their birth dates, or a particular genetic mutation they harbor. There’s a simpler logic at work, though, that’s uncomfortable to plainly acknowledge: to name something endows it with a humanness that makes it much harder to see it suffer, or eventually die. It’s too easy to get attached to a Peanut.
Abstract moral arguments in favor of the use of animals in research invariably converge on insulin, which was first discovered in a series of experiments on dogs in the early 1920s. When it became clear that insulin could more effectively manage the symptoms of diabetes than any of the treatments that existed at the time — which were mostly dietary and only marginally successful — the hormone was extracted in bulk from the discarded pancreases of cows and pigs who were butchered for meat. The shining stars in the literature on the history of insulin are the scientists who worked to purify and mass produce it as a pharmaceutical, but I think about the lone technician strolling into the slaughterhouse at the end of the day to haul away the pancreas bucket. They must have believed that the benefit of this research to humanity was worth the cost they could see and feel and surely smell around them. They had to believe they were doing the right thing. In my experience, at least, it’s very hard to do it if you don’t.
The word compassion has a visceral element built into it. If you break it down to its linguistic building blocks, it means “to suffer together”. Arguably the most galvanizing human experience is suffering, so it’s not surprising that pain is richly represented in our brains. Scores of studies find considerable overlap between areas of the brain that are active when someone experiences pain directly and when they watch or imagine painful things happening to someone else. What’s more surprising is that this isn’t a uniquely human phenomenon. The same parts of the brain that respond similarly to both first and secondhand pain are active in rats when they see another rat in distress.
To study the neural circuitry of learning and motivation, a standard practice is to put a rat in a box, with two levers in front of it. If the rat presses one of these levers, it might receive ordinary food pellets, while pressing the other lever leads to treats. The amount of force or number of presses required to get the more desirable option vary, depending on the goal of the study. Even before the testing phase, though, rats will frequently form mystifying personal preferences for one lever over another. The reasons for this usually only make sense to the rats themselves and are deeply vexing for the people running the experiments, but these baseline preferences also have to be accounted for and can actually provide powerful insights into just how rewarding or unpleasant the task is.
A group of Dutch researchers recently implemented one of these lever-pressing tasks but with a twist: one of the levers produced a reward (some sugar pellets), while the other lever also produced a reward, but at the same time it delivered a painful foot shock to a rat sitting in a box next door. All of the rats caught on to this quickly, and some of them simply stopped lever-pressing because they could see how stressed out their neighbor rat was. Others reversed their preferences, opting to press the lever they liked the least in order to avoid shocking the other rat. There were a few more variations on this theme: sometimes, the lever might zap the other rat, but offer more sugar or require less effort to dispense the pellets. In most cases, the rats would forgo the extra treats if they came at the expense of the other rat. An extra sugar pellet was enough to tip these scales, though: for only 2 pellets of sugar, a rat would avoid pressing the lever if it delivered a shock. 1 extra pellet sweetened the deal just enough that they’d press the lever anyway.
It’s tempting to interpret these experiments as evidence for the transcendental nobility of altruism, an innate trait that hops freely between branches of the evolutionary tree. Minus the moral absolutism, this is sort of true. Our brains share common structures with our evolutionary relatives, like mice or flies or lizards, and these structures behave in similar ways. The total experience of pain, though, is the product of a coordinated effort that engages many different parts of your nervous system, from the sensors in your skin that tell you something is hot and you should take your hand off of it, to your amygdala, the deep-brain structure that drives instinctual fear.
A part of the brain that responds strongly to pain in both mice and humans is called the anterior cingulate cortex, or ACC. The ACC plays a special role in the emotional experience of pain, particularly in people who have to bear it indefinitely, as is the case for people living with chronic illness. Historically, we’ve learned how certain parts of the brain work by observing what happens when they’re broken. Phineas Gage unwittingly taught us how important the frontal lobe is for impulse control when his was smashed in with a railroad tie. We learned that we need the hippocampus and the amygdala for memory formation when Henry Gustav Molaison had large parts of these structures surgically removed to control his seizures, and could no longer make new memories afterward. And when the researchers studying the tendency of rats to avoid shocking each other even if there was a material reward involved temporarily switched off the ACC, they saw this tendency disappear as well.
So on the surface, the actions taken by these animals appear to be selfless. A rat could reward itself with limitless quantities of something it really wants, but it doesn’t, because it’s aware of the distress it causes the rat in the box next to it. At the same time, you could think of it as the most ingenious kind of selfishness: if the part of the brain that controls the emotionally unpleasant aspects of pain are working equally as hard in the rat receiving the shocks as the one delivering them, then the lever pressing rat is choosing just as much to avoid his own discomfort as his neighbor’s.
There are obvious caveats to attempting to map abstract human emotional states onto the behaviors of nonverbal animals. We can’t ask them if they feel sad or sorry for each other, and we can only infer their feelings by anthropomorphizing their gestures and facial expressions, and assuming that these belong to a universal lexicon beyond words. To really study the biology of human emotion, we need humans, and we have a severely limited number of benign interrogation methods when it comes to human brains. The best tool at our disposal is functional magnetic resonance imaging, or fMRI. It’s based on the principle that areas of the brain that are highly active require more blood flow. Because this blood is also traversing a magnetic field, it’s possible to generate a visual landscape of the changes in the strength of the field that occur as a result of the oxygen load of the hemoglobin molecules in your red blood cells.
Once we figured out this neat trick, we were able to stick people into MRI scanners and make them do all kinds of things, for science. The spectrum of these things is extraordinarily broad, running the gamut from identifying the parts of the brain that light up during simple motor movements, to those that are engaged by the contemplation of abstract moral and philosophical problems. Recently, this technique was used to tackle the question of empathy in a set of experiments that recorded neural activity levels in response to pain. The researchers were specifically interested in what makes someone an altruist, so as a working definition of what they term “extraordinarily costly real world altruism”, they looked at the brains of anonymous living kidney donors, comparing their pain responses to those of a matched control group who hadn’t voluntarily given a vital organ away to a stranger.
In the control group, the researchers saw similar patterns of activity both when the subjects experienced something painful (having their finger pinched in a plastic tube) and when they saw another participant experience the same thing. This wasn’t surprising, since many other studies in humans and rodents support this phenomenon of neurological mirroring of pain and the emotions that accompany it. For the extraordinary altruists, though, activation patterns overlapped more strongly during both experiences of pain, and across multiple regions. This group seemed especially attuned not just to the pain of the finger pinch when it happened, but to the fear of an impending finger pinch, neurologically experiencing it as their own fear.
We’re built to intuit another person’s distress, so it seems especially advantageous to be able to deploy this skill when we’re under stress ourselves. In practice, though, when we have our own suffering to deal with, there are limits to our capacity to take on more of someone else’s. Mice are usually more anxious if you put them in a cage with unfamiliar mice, so a group of researchers took advantage of this phenomenon to study the effects of social stress on empathy. When they took pairs of mice who had either lived together for a few weeks, or had never met before, and then exposed one or both of them to a painful stimulus, the pairs of mice who experienced pain together had heightened reactions relative to mice who experienced the same thing alone. In pairs of familiar mice, when only one mouse was experiencing pain and the other was a bystander, pain behavior was still exaggerated relative to single mice. When the mice were strangers, this effect went away.
Now, the researchers ran the same tests but dampened the mice’s stress responses, blocking their stress hormone receptors. When they did this, the strangers behaved more like cage mates when one or both of them were in pain, which implied that the social stress of being around an unfamiliar mouse shut down its ability to share its experience of pain. People behaved the same way, rating pain intensity at a higher level when they experienced it with someone they knew.
This behavior makes good evolutionary sense: if someone else’s experience of pain is intertwined with your own, you’re probably less likely to hurt them, and more inclined to protect them. Reinforcement of social bonds is key to survival, to building families and expanding social networks. Similarly, a certain wariness of strangers and a disconnection from their pain might help separate you from people or groups of people who mean you harm. The social schemes and biases we have are purposeful, helping us to act quickly in situations where careful consideration could cost us our lives. In this sense, though, and in the present day, they could also be thought of as evolutionary time-lags; throw-backs that pit us against each other in the service of survival imperatives that don’t exist in the ways that they used to.
I started writing this before the world changed irreversibly, and it changed really fast. A month ago, the idea of altruism still seemed remarkable from a neurobiological and psychological perspective if only because it seemed hard to conceive of someone who could pick a stranger at random and form a complete enough mental representation of that stranger’s inner life that the force of that person’s distress would move them to give up one of their kidneys. Take a second and scroll through Instagram or Facebook. Now, try to think of any other moment in your life when you’ve idly wondered what one of your friends or professors or colleagues were up to and immediately knew the answer, because you were doing your own personal version of exactly the same thing.
There’s a weird kind of bare intimacy in watching Jeff Goldblum read Dr. Seuss books from whatever house he’s planted in, while from across an arbitrary distance I’m also planted in a house, and we’re probably feeling similar uncomfortable mixtures of incredulity and panic and despair and numbness and grief, right alongside millions of other people who just don’t know what else to do. And while none of us can fully understand another individual’s experience of the situation we’re all in, each of us can at least attest to the broad generalization that it sucks, whatever that looks like up close. Optimistically, I’d like to think that the kind of neural perspective-taking that comes with so-called extraordinary altruism might be pulled closer to the realm of the ordinary by relentless and ubiquitous global crisis. But maybe it’s a comfort just to know that while you might feel like you’re singularly screaming into the void, the void is actually getting pretty noisy right now.