Up and out with Peggy Mason

In late February of this year, a few journalists emailed Peggy Mason asking for comment on “reviving-like” behavior in mice. A paper had just been published in Science describing a mouse approaching a familiar but unconscious mouse and performing a series of escalating actions upon it: grooming, biting its mouth and finally biting and pulling up on its tongue.

These actions, according to the paper, indicated prosocial behavior, in which one mouse was actively trying to benefit another. The journalists wanted to know what Mason thought of it.

“I’m sorry to say it, but it’s nonsensical,” says Mason, who years ago helped propel the rodent prosocial behavior field forward. The behavior seen in the work was real, she says, but she disputes the “interpretation of it,” despite studies published this year in Science Advances, Science and the Proceedings of the National Academy of Sciences that used a similar behavioral paradigm and concluded the actions were prosocial.

It is not unusual for Mason to be this assertive. She is “disputatious,” says Howard Fields, professor emeritus of neurology at the University of California, San Francisco, who was Mason’s adviser for her postdoctoral fellowship. He adds that she sometimes carries her argument beyond what “is justified by the data.” Now, her opinionated nature is bumping up against a portion of the prosocial subfield that is not in line with her way of thinking.

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ason, professor of neurobiology at the University of Chicago, is currently on sabbatical in the Sunshine Coast region of British Columbia, Canada. She spends a portion of her days on her deck, which is decorated with wind chimes, mirrorballs and an electric-powered water fountain, and in the garden, tending to vegetables, herbs and flowers. She has a home office filled with books—including her own textbook, “Medical Neurobiology”—as well as family photos, a large art collection and framed pictures of all the cats she and her wife, artist Gisèle Perreault, have had over their nearly 40-year relationship.

On her computer are two in-progress manuscripts concerning rat empathy and prosocial behavior research. Mason closed her rat lab in May. She has studied empathy and prosocial behavior in rats for about 17 years, but she mostly funded it through private foundation  awards. She will still teach—David Zhu, a recent University of Chicago graduate in neuroscience, says Mason treated students “as her equal,” but never minded “interjecting” when she felt they were wrong—and in the fall she plans to run a neuroanatomy class for a study-abroad program in Paris. But she’s changing course from her rat research on helping and empathy.

The prosocial behavior field began in humans and then primates, long before Mason was around. Meredith P. Crawford’s 1937 experiment in chimpanzees helped define the field, showing that the animals demonstrate helping behavior. But the field really took off with the work of Frans de Waal, who showed, most notably in 1979, peacemaking behavior in chimpanzees.

Russell Church started the rat prosocial behavior field in 1959, with contributions by George Rice and Priscilla Gainer in 1962, but it went mostly silent until 2006. That’s when Jeffrey Mogil and his colleagues published a paper in Science showing that in response to pain stimuli, mice are susceptible to “emotional contagion”—the spread of the same emotion across a social group.

Mason was in her own lab at the University of Chicago studying the neural mechanisms of pain modulation at the time, and in a commentary supporting Mogil’s study, she is quoted as calling it “biologically implausible” to imagine that empathy arose, de novo, in primates. There had to be an evolutionary advantage to empathy in other animals, she reasoned, specifically in animals besides humans and primates.

The commentary on Mogil’s work was Mason’s first public foray into prosocial behavior research. Then, like now, she was trying to interpret the data through natural history, not human emotion. “You won’t understand anything fully until you’ve figured out how it evolved and how it could have evolved,” she says.

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ason, by her account, had a “fabulous” childhood. She was born in 1960 in Washington, D.C. Her father was a lawyer, and her mother ran an art school. She has two older brothers, and the family often discussed politics around the dinner table—the first place Mason learned to use facts to bolster opinion, she says. She has also had a lifelong interest in animals, often visiting the Smithsonian Museum of Natural History as a child, soaking up the principles of evolution and repeatedly taking a taxidermy class there.

She began college in 1978 at Harvard University, intending to specialize in ecology and evolutionary biology. But after two and a half years at the university, she left. “Basically, I took a year off to come out,” Mason says. She spent that time working at a pizza restaurant and bookstore but also volunteered at the Smithsonian Tropical Research Institute in Panama for a project on bat demographics.

Mason had become part of Boston’s lesbian community, but accepting the truth about her own sexuality was “a process,” she says. She told just some of her friends, most of whom were outside the university, and eventually her parents.

That news was initially a “profound disappointment” to her mother, she says, and when she went back to Harvard—and then during her Ph.D. program in neurobiology at Harvard Medical School—she kept that part of her identity to herself. People were getting “beat up” for their sexuality at the time, she says. In October 1986, advocacy organizations presented data to the U.S. government about the rising violence against gay and lesbian communities.

Mason met Fields at an annual neuroscience meeting, and, believing him to be one of the most interesting thinkers within pain research and a “leader of the field,” she discussed joining his lab as a postdoctoral fellow. Being in the closet had become “onerous,” she says, so about a year later, as she was set to transition to Fields’ lab, she told him she needed him to know “one thing,” that she was a lesbian. Fields barely shrugged, Mason says, and today he says he doesn’t even remember the specifics of the interaction. When she joined his lab in San Francisco, where the gay and lesbian community was much more “integrated into society,” she says, she did not feel unsafe anymore.

By the time she moved to Chicago in 1992, she had realized people exhibiting discomfort with her sexuality was “not my problem; it’s their problem,” she says.

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ason fully entered the prosocial behavior field thanks to Inbal Ben-Ami Bartal, now professor of psychological sciences and neuroscience at Tel Aviv University. Bartal saw a commentary from Mason in Scientific American and reached out in hopes of collaborating.

In 2011, they, along with neuroscientist Jean Decety, published a paper in Science showing that rats would consistently open a door to free a familiar cagemate trapped in a tube, even when the trapped rat was released into a separate cage, and thus neither animal received the social reward of companionship. The researchers also did an experiment with two restraining tubes in the cage—one with a trapped rat inside and the other with five chocolates. The free rat would open both and often seemed to share the chocolate with its cagemate, Mason says.

The work made a splash amongst neuroscientists, animal researchers and even the general public. The reaction to the paper was “insane,” says Magnus Blystad, associate professor of biological psychology at Oslo New University College. His university sent out an institute-wide email concerning the study, he says, though he first saw it being passed around on social media. This initial work has gone on to be a “field-defining paper,” says Robert Froemke, professor in the otolaryngology and neuroscience departments at New York University Grossman School of Medicine. “Everyone should know that paper,” he adds.

When Mason’s paper was first published, Timothy Hackenberg, then professor of psychology at Reed College (he has since retired), canceled his comparative cognition class’s readings for the day so they could turn their attention to Mason’s work. “I thought it was a really interesting, novel paradigm,” Hackenberg says. But the class discussion yielded a different interpretation of the results: “while the authors of the original studies see empathy and altruism, we saw social reinforcement,” he says.

Similar to Hackenberg and his class, the field started to drill down on the concept of empathy in rodents. A critique first made in 2012 in the journal Biology Letters began to garner wider attention. The article suggested that Mason’s constrained rat work did not provide evidence of empathy.

Mason and her colleagues later tested the role of individual familiarity versus familiarity to type in rats by pairing the albino strain of rat they used, Sprague-Dawley, with non-cagemate Long-Evans rats with black and white fur. The albino rats would not help the Long-Evans rats unless the two strains had previously lived together for two weeks. Also, the Sprague-Dawley rats would help any Long-Evans rat after they had gotten to know the first one.

Mason and her colleagues then showed in a 2016 study that when a rat was given midazolam, an anti-anxiety drug, it would not open the door to free a trapped cagemate but would open a door to access chocolate. In other words, the rats were not too sedated to open doors but rather were no longer motivated by the distress of the other rat, Mason says. (Control rats would open either door.) This, Mason says, showed that empathy is necessary for motivating prosocial and helping behavior in rats.

But two years later, Hackenberg and his colleagues published a study showing it is social reinforcement that motivates rats to free a trapped cagemate. His lab replicated Mason’s paradigm but used a lever press to open the door. Rats would consistently press the lever, earning a period of social interaction, but when the lever was altered to no longer open the door, they stopped pressing. Another study, published in 2020, showed that rats would willfully enter a restraint tube, even after previously being trapped in one, suggesting that perhaps being trapped wasn’t all that stressful, and disproving “accounts of rat empathy based on the thesis that tube restraint distresses occupants.”

Overall, Hackenberg says he doesn’t like the use of the word “empathy” to describe nonhuman animal behavior. “There’s this implication that it’s like what [humans] experience, and I don’t think it’s anything like what we experience,” he says.

Like Hackenberg, Ewelina Knapska, professor at the Nencki Institute of Experimental Biology, says that humans have “much more developed cognitive abilities than rats.” Blystad agrees with that. “No matter how you place the tube and what you do, you will never reach the stage where you’ll be able to say that this has to be empathy,” he says. Researchers cannot understand what motivates the rats, he adds, so defining the behavior as empathy would require creating a specific observational definition.

In the decade following Mason’s 2011 paper, the work became “more controversial than anything before or after,” Mogil says.

There have been about 20 years of dedicated work in rodent prosocial behavior. Because the field is “very young,” it is still working to determine the “precise language” around describing these behaviors, Knapska says. And there is no “perfect” model to definitively show these behaviors, says Scott Russo, Leon Levy Director of the Brain and Body Research Center at the Icahn School of Medicine at Mount Sinai.

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espite this criticism, Mason’s interpretation of the behavior in the 2011 trapped-rat experiment has not changed. She gets frustrated with those who argue for human exceptionalism, the idea that empathy cannot be assigned to nonhumans. In that world, “animals get to be attached, but they can’t have empathy,” she says.Yet Mason does have her own definition of empathy: It is not necessarily good or bad; it is only the sharing of affective or cognitive experience. What has changed about her earlier work, she says, is her thinking around the use of the word “prosocial,” which suggests a positive intention. “I don’t really believe that prosocial exists out there,” Mason says.

She is not the only one parsing the language of the field. Disagreement around describing behavior is a “tension that runs through all of psychology and all of comparative cognition,” Hackenberg says. Blystad says that simplifying the “many different kinds of motivations” into “empathetic response, prosocial response,” is perhaps more confusing than clarifying.

This gets at Mason’s criticism of the prosocial behavior field as a whole: It “has a little bit too much of a pony in the race.” The job of science is to discover, not pick and choose the explanations that are preferred, she adds. This is, in part, why she disagrees with the interpretation of the recent “reviving-like” behavior studies. Viewers simply want to see it as one mouse reviving another, she says. In a recent article published in Lab Animal, Hiroyuki Arakawa, assistant research scientist at the University of Michigan Medical School, agreed that there is “no logical evidence” that the mouse is trying to “revive an unconscious peer.”

Though she has closed her rat lab, Mason still has one collaboration on prosocial work ongoing and is open to more. Otherwise, she will finish her two papers and continue her study of somatosensation in humans. And she’s not all that interested, anymore, in chasing big journals or constantly conforming to the constraints of academia. “I would, truthfully, publish things on my blog or on bioRxiv and walk away,” Mason says.

Statements like that are what make Bartal say Mason has “chutzpah.” Nicolas Zerda Afanador, a former University of Chicago student and mentee of Mason’s, calls her “completely fearless.”

But Perreault, who met Mason in 1986 and married her in 2006, and who may know her best, is more blunt: “She doesn’t give a fuck what people think about her.”