The science of empathy & sociology of affective neuroscience
A fascinating article in Science this week provides evidence that purports to show mice are capable of experiencing empathy. Langford, Mogil and colleagues found that mice administered a painful injection displayed increased writhing behavior (a reflexive response to pain) in the presence of cagemates who had also been injected than in the presence of either untreated mice or mice that had been treated but were unfamiliar. Moreover, the facilitatory effect on writhing increased in magnitude the longer the paired rats had previously been caged together. The authors suggest that the effect likely represents an empathetic response: seeing a familiar mouse writhing in pain primes pain-related neural pathways in the onlooking mouse, which are subsequently activated more strongly when the onlooker receives the injection itself.
What I think is really neat about this study (beyond the general ‘that’s nifty!’ factor) is the number of different literatures it bears a relation to. Some of these are alluded to by the authors in the article, e.g., recent work on ‘mirror’ neurons. Mirror neurons are populations of neurons that increase their firing rate both when a specific action is performed and when the same action is passively observed in another person or animal. Mirroring systems have been already identified in humans and other primates for a range of behaviors (e.g., certain areas of premotor cortex are responsive to both performed and viewed hand actions), but the implication here is that even mice have at least a rudimentary mirroring system that can enable something like the social facilitation of pain. From an evolutionary standpoint, this makes perfect sense, of course. A mouse that feels a certain measure of distress when it sees a conspecific suddenly writhe in agony is a mouse that’s probably going to be a little more vigilant for threats in the environment, enhancing its odds of survival in potentially dangerous situations. But it’s a long way from evolutionarily plausible stories to hard data. What Langford et al.’s data suggest, along with other emerging evidence, is that some degree of mirroring may be a relatively primitive feature of the mammalian cognitive architecture.
The Langford study also breathes new life into the perennial philosophical question as to whether animals have feelings. Over at Pure Pedantry, Jake Young suggests that whether or not you think mice have empathy depends on your definition of empathy. Specifically, he focuses on the role of abstraction:
If your definition is that empathy is any commensurate change in behavior response to the perceived feelings of the other animal, then, yes, I would agree that the mice are feeling empathy. … On the other hand, if you define empathy as the ability to abstract another individual’s point of view from sensory data about them, then I don’t think this proves mice have empathy. It is clear that mice do not perform this level of abstraction. Mice could not, for instance, feel empathetic about another mouse from a story they heard about it.
I think this is an interesting way to frame the issue, but I think it also omits a third potential definition, which I suspect is the one most lay people hold–namely, that empathy is a specific kind of subjective experience that tends to make you want to act in certain ways. Naturally, this definition makes direct measurement of empathy impossible (which may be why Young doesn’t mention it): we don’t know what (if anything) mice feel, so we have to rely on their behavior as a rough index. That wouldn’t necessarily be a terrible thing, except that in practice, people (scientists included) often apply very different evidentiary standards to animals than to incapacitated humans or infants who may show a similarly restricted range of behavior. When a dog bares its teeth and growls, we refer to it as aggressive behavior, but many people are loathe to say the dog actually feels angry. In contrast, when a 6-month old infant cries and flails its arms, we don’t hesitate to make the latter attribution, even though the baby is just as incapable of expressing its frustration in a more abstract way.
This double standard matters for a couple of different reasons. For one thing, if we don’t apply consistent standards, we risk making the hypothesis that animals have feelings practically unfalsifiable. If the only evidence we’d accept for the existence of feelings in animals is verbal report or some other symbolic representation of emotion, we’re obviously out of luck. Now this isn’t necessarily a bad thing; but if we adhere to this position, we should at least have a reasonable explanation for why it’s ok to sacrifice a dozen monkeys in an electrophysiological study but not to euthanize a 2-month old infant. (Note: I’m not suggesting the two are equivalent, and I’m not arguing that animal testing is a bad thing. My point is just that one’s position on the subjective lives of animals has important implications for other domains, and these shouldn’t be brushed off just because they might be unpleasant to think through.)
A second, even more important reason we should seriously contemplate the notion that animals have feelings much like our own (though presumably less elaborate): failure to attribute emotions to animals is likely to result in the view that there’s something special and mysterious about human emotions, something that can’t be explained by studying animal models at all. And that would have a serious and negative impact on the scientific study of emotion.
Notice that most neuroscientists would find an analogous view absurd if applied to other domains of cognition. No one doubts that most other mammals really see the world roughly the way we do (subject to differences in sensitivity to various wavelength, etc.); no one questions the fact that studying the visual systems of cats and monkeys has taught us an incredible amount about the human visual system. And yet, the notion that emotions should suffer the same scientific fate somehow seems counterintuitive to many people. Neuroscientists who have no trouble discussing what their animals see, hear or sense in published articles get cold feet when it comes to emotions. I think no one’s summed up this sentiment better than Jaak Panksepp, an eminent neuroscientist now at Washington State University. Here’s a quote from a recent article:
The current neuro-behaviorist agenda, ascendant in the 1980s, led to a psychologically impoverished view of ‘‘emotions’’ in behavioral neuroscience, while yielding an enriched understanding of how emotional learning occurs in limited areas of the brain such as the amygdala (LeDoux, 1996). Most emotional processes that actually exist in animal brains have been disregarded (see Blanchard et al., 2001a for a sampling of modern behavioral neuroscience views of emotions). The failure of neuro-behaviorists to accept a diversity of emotions and the corresponding affective experience as a key aspect of animal brain functions has reduced the likelihood of useful cross-fertilization between animal and human studies.
Joseph LeDoux, the best funded animal emotional–memory researcher in America, publicly related how he failed to obtain approval for his initial grant applications until he extracted the term ‘‘emotion’’ from his proposed work to study classical-conditioning of fear and replaced it with learning and memory terms (see Panksepp, 2002). Other neuroscientists interested in emotions had comparable, but more sustained, funding problems throughout the last quarter century.
I’ve been a huge fan of Panksepp’s work for a while now. I find his arguments cogent, his theoretical models much more sophisticated than most, and his experimental work meticulous. And yet, despite being relatively well-known (largely as a result of his 1998 book Affective Neuroscience), Panksepp’s work–which spans several decades and a broad range of affect-related topics–hasn’t been nearly as influential as one might expect.
I can think of at least three reasons for this. First, most of Panksepp’s work has proceeded at a much lower level than people interested in emotions are generally comfortable with. Unlike domains such as vision, where it’s been clear for a long time that the phenomenal structure of vision is very different from the structure of the underlying mechanisms (there isn’t really a little man in your head flipping channels on a big screen), many people still don’t seem to believe that studying emotions at a systems neuroscience level is a fruitful approach.
Second, to some degree, behavioral neuroscientists have a vested interest in differentiating between human and animal emotions and denying the latter, because it’s easier to operate on a subject you don’t think feels much of anything. And third, the current dogma in affective neuroscience is one of simplification and dimensionality. There’s a strong focus at the moment on dimensional models, e.g., Richard Davidson’s famous hemispheric lateralization model (approach-related emotions are associated with greater left PFC activity, withdrawal-related emotions with right PFC activity), or Russell and Feldman-Barrett’s affect circumplex (which holds that most of the variance in emotions can be captured by just two orthogonal dimensions of valence and arousal). The main appeal of these theories is that they’re simple. You can explain their rudiments in a couple of minutes, and they’ve produced an inordinate amount of empirical research over the last three decades. Unfortunately, they’re also (at best) incomplete. No dimensional model I’ve seen does a passable job of explaining how one gets from 2 (or 3, or 4) dimensions to the full range of emotions one can experience and reliably distinguish between without a lot of vague hand-waving.
In most respects, Panksepp’s work is the antithesis of all of this. His models are extremely complex, drawing on an intricate knowledge of low-level animal circuitry; his avowed position is that human emotions depend largely (though certainly not entirely) on mechanisms present in other mammals too; and he emphasizes a ‘basic emotions’ perspective that argues that emotions are best understood in terms of a small number of core biological systems each associated with several emotions rather than abstract low-dimensional psychometric models. As a result of this contrarianism, his research has been relatively marginalized. (The fact that his writing is extremely opinionated and critical of other work probably doesn’t help, either.)
What does all this have to do with empathy? Well, personally I think Panksepp’s approach is the right one. And I think there are few enough examples of affective neuroscientists adopting the view that continuity exists between human and animal emotions that I think it’s noteworthy when a study is published that offers substantial support for that position. I think that studies like Langford et al. are fascinating in no small part because they provide a tantalizing glimpse into the neural substrates of emotion and offer us the hope that feelings aren’t intractably complex or unique to our species. They suggest the possibility that even a complicated emotion like empathy could potentially be explained by appeal to relatively simple properties of our cognitive architecture–properties potentially shared even by dogs, cats, and mice.
Based on Langford et al., one can tentatively suggest the possibility that appeal to a mirroring system might be all that’s necessary to explain a large subset of episodes we’d have no trouble labeling ‘empathy’ on a day-to-day basis. For example, take the immediate emotional reaction most people experience when they see someone sitting alone and crying. How different are such cases from mice writhing in pain? Well, a certain part of most people (myself included) immediately wants to shout “Very different!” But it’s not the scientific part; it’s a part that simply finds it hard to believe a relatively simple, seemingly reflexive behavior in a rodent could have much in common with the rich, complicated emotion we’ve all experienced first-hand. Ignore that visceral response and you can see the parallels. In both cases, what you really need is a mechanism that allows visual information to activate emotional pathways in much the same way they’d be activated by the corresponding first-hand experience. The rest falls into place given the prior existence of more basic pathways for various forms of pain processing. Far from being ludicrous, from a scientific standpoint, this hypothesis is an elegant and parsimonious one that could easily generate novel testable predictions. (For instance, electrophysiological recording could be used to attempt to identify the locus of the effect in mice, and the results then compared with human neuroimaging data in similar paradigms).
Now, I certainly don’t want to give the impression that I really think empathy in humans really is no more complex than in mice, or that the Langford paper offers a conclusive take on the matter. I don’t, and it doesn’t. My point is just that people–yes, even scientists!–have a deep-seated tendency to view emotion through different lenses than other domains of cognition, and it colors the way we approach our research. What in other domains would be seen as a clever experiment that opens the door to interesting avenues of research runs the risk of being dismissed out of hand in the field of emotion research as speculative and fantastic. And that would be a shame, since it is a clever experiment that opens the door to interesting avenues of research.