Sarah Feng ’25 knew her rats intimately. She worked as an undergraduate researcher at the Arnsten Lab, a neuroscience lab at the Yale School of Medicine, from August of 2023 to August of 2024. She investigated how different chemical stressors, including cocaine, affected the prefrontal cortex — the part of the brain responsible for abstract thought — by experimenting on rats. For six months, including this past summer, she trained, socialized, and cared for the rats in her lab. “You know their personalities,” she says, “because rats are very particular and intelligent.” She brings up that some come out of their cages less reluctantly than others, displaying levels of confidence, and that many can memorize layouts of mazes in their heads for several minutes at a time, displaying intelligence. After the rats became habituated to humans, she would pass them off to other researchers, who would treat them with the chemical stressors.

“Then you kill them, and that’s it.”

After my conversation with Feng, I had to wonder — what is it like to hold life and, in some cases, mete out death with your hands?

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Odessa Goldberg ’25 worked with mice, not rats. On Beinecke Plaza on a busy Friday, she comfortably discusses how she used to slice mice brains as a part of research to discern how physiological conditions and changes to those conditions affect brain function.

Slicing brains was Goldberg’s main job at the laboratory, though she occasionally fed mice, too. The intact brains were stored in negative-eight degrees Celsius freezers, packed in boxes like the ones “you get cheap jewelry in,” wrapped in tinfoil, and coated in a gel that preserved their integrity. Once Goldberg took the brains out of the freezer, she would have to slice them quickly, but carefully. The brains could not melt, but she also needed the samples to be viable — that is, cut well. With a gray, bladed machine called a cryostat, she cut brain samples while keeping them frozen at negative-twenty degrees Celsius. Then she would place the freshly cut slice onto a slide for further detailed analysis.

Goldberg had “practice brains” that were, in fact, real mouse brains — they were just not meant for research data. A mouse brain contains “powerful information that you don’t want to be wasteful with,” she says,  “and you want to treat it with the respect it deserves.” Throughout her time at the lab, she became focused on perfecting the practice of brain slicing. But, as she repeated the process over and over again at her job, the slicing became rote; her body did the work automatically.

She broke the routine on her twentieth birthday. As she was cleaning the cryostat, she forgot the machine was still on, and it cut off part of her pinky finger.

“And my first thought was, ‘Do I need to keep studying this?” she says, laughing a little bit in retrospect. However, the moment changed the way she thought about slicing mice brains. “It made it feel very much more real.” She became very cautious and aware of what she was doing after that experience.

Goldberg no longer works at that laboratory. She now conducts research that uses human models, which she prefers. She does not work with humans the way that she worked with mice, to say the least; she does not slice human brains. Animal testing “doesn’t feel like a great moral activity,” she says. But, she concedes, “then again, I’m not a vegetarian. I consume meat, and it’s not even for the higher purpose of science.”

By working at her former lab, she gained a new respect for mice. “I don’t really think of them as a pest or something,” she says. “Except, you know, I had many mice in Branford.”

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“You and the rat are the only thing in there,” says Feng. “And you just look at it, and it looks at you.” She did not kill the rats herself; her job was to habituate them for six months in a basement room at the Yale School of Medicine, which she describes as a “clinical,” windowless white box that played white noise. 

Over the months, Feng grew closer to the rats. She learned to differentiate between them according to their particular quirks and behaviors. Some rats looked at her with more intimacy than others. Some appeared more confident or displayed more anxiety. They were named in a kind of code. “We’d be, like, SU6 is really smart.” Feng says. Through playing and socializing, rats relied on her and the other researchers for comfort.

And then she watched them die. “You’re like, oh my god, I’m a terrible person,” she recalls thinking.

Feng maintains that animal models were necessary for her research, as well as for other neuroscience projects: brain systems are simply too complex for synthetic models to produce viable, scientifically significant results. She mentioned examples of treatments for diseases that could have only existed because of animal testing; one such is guanfacine, which was developed in the Arnsten Lab, and which now treats hundreds of thousands of cases of ADHD and schizophrenia. The development of guanfacine used macaque monkeys as research models.

I ask Feng if she might assume the rats to be more “human” than they actually are, that we might attribute familiar emotions, feelings, and thoughts to them because they display some social behavior. She doesn’t think that rats have the same level of consciousness as humans, but acknowledges fundamental similarities between human and rodent brains. 

“After you do research, you’re like, ‘oh, they have the same brain areas as us,’” she says, “and then at the end of the summer, you’re like, ‘oh wait, they have the same brain areas as us.’”

Via text, Feng told me that some researchers have quit shortly after working with animals, due to feeling uncomfortable with the process. Working with very human-like animals, such as macaque monkeys, can be especially hard and is more likely to push away researchers. However, there remain many researchers who accept the emotional difficulty and still work with animals. Dr. Stephen Latham, Director of Yale’s Interdisciplinary Center for Bioethics, analogized the situation with his wife’s family’s neighbors in rural Scotland, who raise Highland cows for beef. They raise the cows with great care, even though they’re going to slaughter them. If a mother cow dies, they bring the calves into their kitchen and feed them from a bottle. Dr. Latham personally knows lab technicians who love the animals they test on. “They’re incredible,” he says. “They work so hard to keep the animals comfortable.”

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When I was speaking with Goldberg, she recalled the disconnect between the animal-research training that she had to complete and the slicing of the brains. “I had gotten all this training not to kill them,” she says, “and then I’m slicing dead mice.” If all goes well, Goldberg’s research will have helped make people’s lives better. But how does one think about the distant future when mice brains are right in front of you, sliced into pieces?