The Brain from All Sides

How do we see? How do we think? How do we feel? Our brains are pieces of equipment, and like any other equipment, they must work mechanically. Two graduate students in the Physics of Living Matter lab headed by Lasry Professor of Physics Vijay Balasubramanian are taking different approaches—informed by their different backgrounds—to learn more.

John Briguglio came to Penn from Carnegie Mellon with a wide-ranging interest in physics, especially biophysics, trying to understand the physical mechanisms that allow biological systems to function the way they do. The second-year student is currently working on a project examining the hypothesis that our sensory systems are tailored to the environment we were exposed to as we evolved. “We are trying to understand how the brain or eye perceive textures,” says Briguglio.

He is helping to characterize images of the natural landscape in Botswana—where it is thought that humans evolved—according to the textures they contain. In collaboration with a group at Cornell that is testing how our eyes react to specific textures, he is examining how well those textures characterize the natural scene. He says, “We would predict that the textures we’re sensitive to seeing are exactly the ones that characterize these natural images well.” It’s still early, but results are looking positive.

“If you truly want to describe a complicated phenomenon, the only language, in my view, is mathematics.”

Psychology graduate student Xuexin Wei studied mathematics in China, but was also interested in how the brain works. While in college at Peking University he found he could combine the two, using mathematics to study brain function: “If you truly want to describe a complicated phenomenon, the only language, in my view, is mathematics,” he says. Now in his third year at Penn, Wei is investigating spatial representation—how we see and navigate through space—in the brain. Scientists have recently discovered that an area of the brain, the Entorhinal Cortex (EC), sends spatial information into the hippocampus. Interestingly, he says, rather than individual neurons responding to one point in space, neurons in the EC respond to a set of spots arranged almost perfectly in a hexagonal lattice.

“It’s a weird thing, actually, why it wants to use the lattice to represent the environment, rather than on a point-by-point basis,” says Wei. Using mathematical models, though, they discovered that the lattice would be the most efficient way to represent space. “The trick is that the lattices have different scales, and collectively they can form a map of the space,” Wei says. The theory also predicts that the ratio between adjacent scales should be determined by Euler’s number, a mathematical constant. “Euler’s number may be the most famous mathematical constant,” Wei says. “It’s amazing that we find it in a biological system.” Psychologists and neuroscientists have discovered that there is a tight link between memory and spatial representation; Wei hopes that their work will provide some insight into how the memory works.

He and Briguglio both continue to expand their own horizons, as well. Along with psychology and neurosciences, Wei enjoys discussions with people from the math department and with statisticians at Wharton. From physics, Briguglio is building connections with neurosciences. “Physicists like to write down a lot of theories and models of things,” he says. “But especially for working with biological systems, it’s extremely important to really be in touch with the experimental side.”