Neuroscientists Christian Keysers and Valeria Gazzola have built their careers on an idea that most of us accept but that is hard to pin down scientifically: that subtle, often-unconscious cues and perceptions—intuitions—offer insight into another person's feelings and behavior. It's commonly called empathy. A classic example, often cited in talks by Keysers, is the scene in the movie Dr. No where a tarantula crawls up James Bond's arm; while watching the scene, many observers feel the same fear and disgust (though perhaps less intensely) that they would feel if the spider were crawling up their own arm.
Such concepts “feel so immaterial that you think it’s beyond science,” Keysers says. But Keysers and Gazzola, who are married, are making these concepts more tangible at the Social Brain Lab at the Netherlands Institute for Neuroscience  in Amsterdam.
Growing up in Belgium, Keysers was interested in physics, philosophy, and psychology. In Italy, Gazzola was drawn to the arts and the sciences, including the human mind and behavior.
Keysers obtained a master’s degree in psychology with a minor in biology from the University of Konstanz in Germany in 1997. He then joined the School of Psychology at the University of St Andrews  in the United Kingdom to do a Ph.D. with David Perrett studying facial recognition in macaques by recording the electrical activity in single neurons.
After finishing his Ph.D. in 2000, Keysers did a postdoc with Giacomo Rizzolatti in the Department of Neuroscience at the University of Parma  in Italy. Rizzolatti was one of the scientists who discovered mirror neurons—neurons that activate when animals perform an action, but also when they observe someone else performing a similar action. The idea that the brain could mirror what is going on in others generated a lot of enthusiasm among researchers; it was recognized as a potential neural basis for empathy. At Parma, Keysers helped identify mirror neurons that were activated not only when the monkeys observed an action but also when they heard a sound associated with it . The research led to a 2002 paper in Science.
Keysers and Gazzola met around that time during classes at a climbing gym. Gazzola had just started a master’s degree thesis at the university, investigating the physiological consequences of stress in rats. Soon, they were spending a lot of time together, but apparently it wasn't enough: Keysers encouraged Gazzola to visit the Rizzolatti lab, hoping that she would join. She signed on, cementing a close scientific and personal alliance that has lasted for a decade.
For her thesis in the new lab, Gazzola studied mirrorlike phenomena in humans using functional magnetic resonance imaging (fMRI). She found that brain regions activated by touch also respond when a subject observes someone experiencing the same sensation . The work, which was done in collaboration with Keysers, led to a 2004 Neuron paper.
As their time in Rizzolatti’s lab was nearing an end, Keysers was offered a tenure-track position at the University of Groningen’s NeuroImaging Center  in the Netherlands; Gazzola was offered a Ph.D. studentship. Despite their difference in rank—Gazzola was Keysers's Ph.D. student—they worked together to set up the lab and “worked again as peers on joint projects,” Keysers writes in an e-mail to Science Careers.
“When we first came across the notion of mirror neurons, and the fact that you don’t really just think about what others do but that you kind of enact it in your own body, that was such a powerful and elegant way to capture this kind of immediate sense of intuition that you have in everyday life,” Keysers says. “It’s our foot in the door of the mind.”
At Groningen, the lab used fMRI studies in humans to extend the concept of the mirror neuron to what they call “shared circuits”—neuronal circuits that are activated not only when we perform an action but also when we observe someone performing a similar action. Keysers and Gazzola started out studying the shared circuits that mirror action, sensation, and emotion independently. But they soon found evidence of mixing: The brain mirrors the sense of touch, for example, when a subject observes someone else performing an action where touch plays an important role.
This led the couple to hypothesize that the shared circuits for action, sensation, and emotion are “all working together to give you a … more complete perception” of another's behavior, Gazzola says. “They are one system basically." Depending on the context, some areas are activated more or less than others.
This system could be the fundamental component of the empathic brain, Keysers and Gazzola believe, and they are now working to confirm this hypothesis. The lab is trying to tease out the contributions of the different shared circuits in determining how we perceive others, and how those circuits interact. They are also working to understand how the mirroring system contributes to social experiences and psychiatric disorders. Recently, they‘ve recommenced animal studies, which Keysers says are necessary to map “a more detailed wiring diagram, in terms of what neurons speak to what neuron with what neurotransmitters.”
The couple works together closely in a way that mirrors their research topic: There is a lot of mixing, a lot of shared brain activity, and a lot of empathy. They appear to have little interest in working independently. “We could really share the burden, share the insecurities, and, therefore, I think, build a much stronger lab,” Keysers says.
After completing her Ph.D., Gazzola did a postdoc in Keysers’s group. But even as a Ph.D. student, she helped build the lab and served as a supervisor, which, she says, was challenging. Their early graduate students "embraced both of us equally because we had developed a technical expertise in fMRI that no one had at that time,” Keysers writes in an e-mail. By the time Gazzola was halfway through her Ph.D. and new students started joining the lab, she “had indeed already collected a level of expertise and maturity that made people trust her advice."
Gazzola and Keysers have taken on complementary roles in the research. “He’s more like the seller; I’m more like the devil’s advocate,” Gazzola says. Upon encountering a new result, “I start to think immediately about the story we can make out of it and how we can sell it to a high-impact journal, whereas Valeria’s usually the one that tells me, ‘Well I don’t trust the results yet,’ ” Keysers says. If they were working separately, Keysers and Gazzola would each have to fill both of these roles, but together “we make an even stronger synergy,” Keysers says.
Their approach may raise some eyebrows, but it seems to be working. “He is definitely one of the most brilliant cognitive neuroscientists of his generation,” and “She is also a very brilliant young neuroscientist,” writes Vittorio Gallese, one of the other discoverers of mirror neurons, who worked with them in Parma where he is still based, in an e-mail to Science Careers. “[They] combine technical excellence with creativity.”
From a career standpoint, Keysers—the more senior and visible of the two—has excelled. It took him just a year to become an associate professor at the NeuroImaging Center. He was appointed full professor 2 years after that. Last month, he won a Consolidator Grant from the European Research Council.
The couple is aware that their professional closeness could harm Gazzola’s career prospects. Nonetheless, she seems on track. Three years after finishing her Ph.D., she was appointed to a 3-year senior scientist position in Keysers's Amsterdam lab, funded by a grant she obtained from the Netherlands Organisation for Scientific Research. She is also on the tenure track at the University of Groningen, where both scientists maintain an affiliation. Their strategy, they say, is now to build close but parallel niches that will lead to a more recognizable profile for Gazzola even as they continue to work together closely.
Part of the motivation for the move to Amsterdam was their wish to stop teaching and hire more postdocs so that they could have more time to start a family. Today, they have a 2-year-old daughter. At home as well, the couple is paying attention to sharing the tasks. "During the week, I cook a little more often than she does … and I wash the dishes a little more, whilst she does the laundry," Keysers writes in an e-mail. "With regard to our daughter, I guess the mix is 60 her, 40 me so far, given that she took maternity leave, and nursed Julia, and takes one day off a week (Wednesday) to be with Julia. For the rest [it's] a rather equal split." They are expecting their second child soon.
Both scientists say that spending time with their daughter has had a positive impact on their research. “It stimulates your mind,” Gazzola says. “We don’t tend to look at her as an experiment, but still you observe a lot of things, and you start really wondering” about some fundamental human questions, she adds. Keysers, in particular, is fascinated by how, in a child’s first year of life, “your understanding of its inner life entirely depends on the kind of non-verbal communication we call empathy—showing us how rich the phenomenon is, and how it develops.”