Neural Roots of Curiosity Explored

How does the intense desire to know take shape in the brain? Simons Society Junior Fellow Jennifer Bussell is designing experiments to study that question

Jennifer Bussell

Simons Society Junior Fellow Jennifer Bussell is designing experiments to study the neural roots of curiosity. Credit: Allan Zepeda

Jennifer Bussell is curious about curiosity. A basic desire to learn about the environment confers an evolutionary advantage on many species, but we humans also seek out information for its own sake. What is it that drives us to know something, just for the satisfaction of knowing it? “That’s a fundamental question that we know very little about,” says Bussell, a postdoctoral research scientist at Columbia University and a Simons Society Junior Fellow. Bussell is just beginning experiments in mice to investigate the neural underpinnings of our desire to find things out. Recently, I spoke with her about her work. An edited version of the interview follows.

Anyone who has had dogs or cats knows that they will investigate a new toy or other object in the room, as a way to make sense of the environment. But how do you scientifically test whether an animal is curious?

In most animals, the drive to get information, the drive to explore, to know or seek information, evolved because usually it’s useful to do that in the environment. But to study this drive — call it curiosity — we have to isolate it from other rewards and artificially make the information gained useless.

My collaborator, Columbia professor Ethan Bromberg-Martin, has come up with a wonderful way to measure monkeys’ desire to gain information independent of other rewards. In one experiment, thirsty monkeys can get a drink of water by moving their eyes to choose a symbolic target on the left or right of a computer screen. The monkey has a 50-50 chance of getting a large water reward whatever its choice. On the right, it sees one of two symbols: One symbol is associated with getting a lot of water, and the other is associated with getting less. On the left, the monkey sees one of two other symbols, neither of which means anything — the symbols on the left are not correlated with the amount of water. So the monkey can choose whether to have information in advance, but its choice has no effect on its water reward.

Once the monkey learns that it can look to the right and know ahead of time whether it will get the larger water amount, it almost always chooses to know. What’s even more amazing is that the same reward-encoding neurons that fire when the monkey gets water also fire when it sees the symbol that gives it information. We’re trying to design a similar experiment in mice.

How can you test information seeking in mice?

Smell is at the center of a mouse’s world. The researchers in the lab I’m in [run by Nobel laureate Richard Axel] know a lot about how the identity of a smell is represented in the brain. In the experiments I am setting up, we will test thirsty mice in a box with holes, or ports, where they can receive water. We will offer the mice information in the form of odors rather than visual cues, and they can indicate their choices by entering different ports. We expect that curious mice will choose the ports with informative odors, and we are interested in how those odors are represented in the brain.

How do you determine whether neurons involved in recognizing a smell are also involved in or correlated with curiosity of that smell and whether it holds information?

We can identify which neurons are activated by an odor using microscope images of a particular fluorescent protein inserted into neurons. Because we can see which neurons fire in response to a smell, we can ask whether different cells are activated in the mouse’s cerebral cortex when the smell signals the possibility of information versus when it does not.

We can also silence or activate the particular brain pathways we think might be involved in driving this curiosity and ask if those pathways play a causal role in the choice of information.

How did your own curiosity lead you to neuroscience?

As an undergraduate, I worked in a lab where we wanted to understand, genetically, what makes humans unique. We looked for brain-specific genetic differences between humans and other primates, so I’ve always been fascinated by the question of how a physical object embodies a mind and consciousness and a drive to understand the world.

In graduate school, I set out to study molecular biology, but then I learned about all of the discoveries being made in neuroscience. It seemed like such an exciting field, and I wanted to be a part of that. That was the first time that I took formal neuroscience classes, and I switched my training rotations to neuroscience. I remember watching fruit flies’ courtship under a microscope for the first time and thinking about how we knew and could, in a way, control the 2,000 neurons that make the insects do that complicated behavior. That was really amazing.

Before going to graduate school, you worked as a management consultant in the biotechnology industry. How has that experience shaped your career?

My graduate school adviser likes to say that, unlike most scientists who spend their entire lives in the captivity of academia, I’ve been out in the wild. Working in the ‘real world’ was really helpful in terms of learning how to work in a team. But mostly it made me appreciate how lucky I am to be an academic scientist. I have so much gratitude toward the taxpayers and other funders for allowing me to think deeply about the brain and how it works, and I really want to be able to do something meaningful with the opportunity.

What questions about the brain do you hope to see answered during your career?

So much about the brain is still mysterious, but one of the big questions is how information is transformed within a neural circuit. We know there are electrical and molecular signals, but what’s the code? Knowing that would be the first step toward understanding the brain in the same way that we understand an electrical circuit or a computer, where we actually know how information processing is accomplished.

Personally, I would also love to know more about the extent to which seeking information is the motivation for animals to do things. Curiosity is starting to seem like an important motivation for learning. If we can understand more about how it works, maybe we can encourage it.

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