Scientist Profile – Professor Mark Howe
Illuminating the deep neural circuits driving motivation and learning
Mark Howe, Ph.D. – Assistant Professor of Psychological & Brain Sciences
The Howe Lab studies how neural circuits motivate and direct actions to reach desired goals, and they have developed optical tools that allow them to study activity in a large structure located deep in the brain—called the striatum—which plays a critical role in such processes.
Professor Mark Howe (Center for Systems Neuroscience, Neurophotonics Center) talked about his research and its implications for treating conditions like Parkinson’s Disease. He also reminisced about going on conservation field studies with his father and shared his fondness for cold-weather football and chili.
How would you describe your research and the goals of your lab?
Our main goal is to understand how neural circuits motivate us to action and direct our actions to reach desired goals. One aspect of this we investigate is how our brains use stimuli from the external world to guide our action through learned associations. For example, on my morning commute, my brain has learned associations between the landmarks that I encounter, like signs or buildings, and the appropriate direction and speed of travel that my car must go to reach my office. Having repeated the route hundreds of times, my brain can now efficiently direct my driving almost without me having to consciously think about it.
Another aspect we investigate is how the brain learns that actions taken in response to certain external stimuli are associated with positive outcomes. For example, you might learn that the logo of your favorite coffee shop predicts a delicious vanilla latte, and so seeing that logo might motivate you to enter the coffee shop in the future.
We want to understand the neural basis of these processes at the level of neural dynamics occurring within specific cell types and specific brain regions, across timescales ranging from milliseconds to days or weeks. And we want to do this in the context of behavior.
How do you study the neural circuits responsible for this kind of learning and action?
The tools we use are primarily optical, meaning they detect and measure light in the brain. These light particles, known as photons, are emitted from proteins that scientists have genetically encoded to act as sensors in the brain. These sensors can target the activity of specific neurons and cell types, allowing researchers to monitor brain activity with great precision.
Our lab focuses almost entirely on a deep brain structure called the striatum, located within the basal ganglia, which plays a critical role in the kind of learning and action processes we investigate. Studying the striatum is challenging, however, because it’s big and it’s deep, so part of what we do is develop tools that are expansive enough to access photon activity across the whole structure yet also precise enough to target specific cell types within that structure.
One tool we developed, in work led by our postdoctoral associate Mai-Anh Vu, is an optical fiber array implant that measures photon activity from the genetically encoded sensors I described. Compared to the larger, single fiber implants that have been used in the past, the fibers we use are tiny, and thus less invasive, allowing us to implant over a hundred individual fibers across the striatum. These fibers can remain implanted for weeks or even months, allowing us to track how neural dynamics change over the course of learning.
Can you give an example of a study that incorporates this tool?
Some of our studies involve the mice running on a spherical treadmill as they navigate a virtual reality environment displayed on screens in front of them. We can monitor their neural activity using the fiber array implant we developed as we simultaneously collect behavioral data related to their actions and decision-making while they navigate the course. In one such study, we found that the same visual landmark can serve to either increase or decrease a dopamine signal in the brain, depending on whether the animal has learned that the landmark indicates it’s going in the correct direction (resulting in an increase in dopamine) or the incorrect direction (resulting in a decrease in dopamine).
What makes this research so important?
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When did you know you wanted to be a neuroscientist?
The first person to influence my journey as a scientist was my dad. He’s an environmental scientist and conservation biologist, and he used to take me out on his field studies where we would look for birds and do various surveys. It was a unique experience that drove my love for exploring and solving scientific mysteries.
I first joined a neuroscience lab in my junior year of college. We frequently stayed till two or three in the morning, eating vending machine food and conducting these very complex experiments involving epilepsy in rats. It was an invigorating, intellectually stimulating experience that shaped my desire to pursue a PhD in neuroscience.
What advice would you give to students entering your field?
Graduate students in neuroscience are often encouraged to acquire a range of skills, like coding and statistics, and to develop and use new technologies. I agree this is important, but I would balance that advice by reminding students not to get so “methods drunk” that they lose sight of the underlying research questions. I get a lot of rotation students who are excited to work with technology like our fiber array or two-photon microscopy, but they are less clear about the foundational knowledge they want to gain from using such tools.
Can you share any hobbies or talents of yours outside the lab?
Like many people, I became very interested into cooking during the pandemic. I wish I’d had this level of interest when I was younger—as a grad student I had a horrible diet and ate 7-Eleven food. Now, I cook all the meals in my family. Chili is one thing I love to make, especially during football season. I’m originally from Green Bay, Wisconsin, and I go back for Packers games every year.
Not surprisingly, as a father I also tend to get interested in my son’s and daughter’s hobbies. Sometimes my son will get passionately into some activity, so I get really into it too, but then he’ll just drop it and move on to other things, but I continue with it. Disc golf is one example—I’m still an avid disc golfer.
Interview conducted Tanvi Agrawal and edited by Jim Cooney.