Occasionally, science looks like the classic stereotype of a white-haired guy alone in a lab late at night, having a Eureka moment. But more often, it looks like biking around Boston with 50 pounds of chocolate sprinkles.
Marlene Cohen, PhD, then studying math as an undergrad at MIT, got her first taste of neuroscience in Matt Wilson’s lab training rats to run on mazes for rewards of “jimmies” (Bostonian for chocolate sprinkles). Ever since then, she’s been trying to understand how our brains take in information about the world around us, and how we act on that information.
“I got hooked on the link between neurons and behavior,” she said.
Cohen, now a Professor of Neurobiology at the University of Chicago, was always interested in the things that impacted how we saw and interacted with the world around us, expressing this interest through a variety of passions. As a child, her mother would catalog what she wanted to be when she grew up, with responses ranging from dolphin trainer to artist to musician.
Now, she gets to be “part trainer, part biologist, part psychologist, part engineer, and part mathematician,” thanks to the interdisciplinary nature of her research in the Neuroscience Institute at UChicago. This community of diverse researchers is a large part of what brought her to UChicago in June 2022.
“One of the great joys of science is getting to know people from all over the world who have backgrounds that make them see the world in a very different way,” she said. “And that's a lot of what we study: how all the different things that make you who you are affect how you see the world.”
Translating the brain
To get at this question, she uses vision as a means to investigate cognition: how signals about the world get transformed in the brain to produce behavior. Humans get a majority of our sensory information through our eyes, making vision important for the guidance of behavior. Additionally, it’s simple to manipulate in the lab. Much of her work involves having subjects sit in front of an eye tracker while performing a visual task on a computer screen. “We know exactly what’s on the screen and exactly where they’re looking, so it’s really easy to quantify things both at the sensory and the behavior end,” she said.
So, that just leaves what’s happening in the brain. Cohen was one of the pioneers of using arrays that measure signals from multiple neurons at the same time. “Having these sensory and behavioral anchors allows us to relate what’s going on in the brain to things that we can control really well,” she said.
Her recent work unites basic science with ideas that are also relevant for the clinic. In simple systems, researchers can use straightforward manipulations to show causation. For example, you can knock out a gene in a mouse to show the lack of that gene has some impact on behavior. Manipulating cognition, on the other hand, Cohen says “is not as simple as turning on a single neuron or even a group of neurons.”
So, she turned to methods that have been used in clinical settings for decades to change aspects of cognition: drugs. In particular, she was interested in the role of attention, opting to investigate methylphenidate – also known as Ritalin – a drug often used to treat Attention Deficit Hyperactivity Disorder (ADHD). Her team found that Ritalin increased performance on visual tasks, but only when subjects were cued to the relevant location in the visual field. Essentially, attention to the correct location was required for enhanced performance. In the brain, this performance increase corresponded to neurons in the visual cortex changing their behavior. As task performance increased, activity of these neurons got more independent from each other. Importantly, Ritalin changed behavior exactly when it changed the activity of these neurons, suggesting the cognitive mechanism of selective attention that this drug hijacks.
In line with understanding how attention affects your behavior, her lab also studies how your belief about the world affects decision making. To study this phenomenon, they trained subjects to identify two different visual features of an object, and then asked them to indicate which one they believed to be relevant to the task before performing it. Researchers looked at how this task-belief and subsequent performance related to one another, and what happened in the brain during the task. They found that stronger task-belief allowed for better task performance, but only if their belief about the relevant feature was correct.
Additionally, Cohen’s team could map the confidence of a subject in selecting the relevant feature onto what was happening in the brain and use this information to guess how the subject would change their behavior in the next trial. Specifically, variability in the response of visual cortex neurons mapped on to the confidence of the subject that they were paying attention to the relevant feature. This then translated into behavior: if subjects were more confident that they were paying attention to the correct feature but performed poorly on a trial, they would switch their strategy for the next trial. But if they weren’t confident in their strategy to begin with, they were more likely to stick with their strategy for subsequent trials.
Whole humans do better science
Cohen’s research all gets at the underlying question of how human behavior is generated based on the different things that define us as individuals and what we see in the world around us. But this interest in human differences doesn’t just stop at scientific research. For her, being a researcher is just as much about being a well-rounded person in a team of other unique people as it is about the phenomenon you’re studying. “Science happens when a lot of different people with different backgrounds and different ideas and different viewpoints come together and try stuff,” she said.
She’s never been the type of person to get so hung up on one research question that she can’t make time for the things in life outside science (a la the stereotype of the mad scientist during the wee hours of the night), but she sees that as a good thing. Cohen believes you can be a scientist and still have a life outside of your research, and your research might be all the better for it.
“It’s not just that we do good research despite our different interests, I think we actually do better when we’re whole human beings,” she said.