Groundbreaking Research Led by Alexa Mousley ’20 Identifies Five Stages of Brain Neuroconnectivity

hen Alexa Mousley graduated from Vassar in 2020 and headed to Cambridge University to pursue her PhD, she was following the passion that first led her to major in neuroscience. As a Vassar student, Mousley was fascinated by brain connectivity and development, and she brought this fascination to her PhD studies, serving as lead author on a groundbreaking paper. Her discoveries could change the way scientists understand how physical connections in the brain form and develop at different stages of life.

Published in November in Nature Communications, the paper “Topological turning points across the human lifespan” reveals five distinct stages of brain development from birth to late adulthood. To pinpoint these stages, Mousley gathered 4,000 MRI scans of individuals from infancy to age 90 from open data sets. By using machine learning to analyze the scans, they found patterns in the data that pointed to marked shifts in brain wiring around ages 9, 32, 66, and 83.

Mousley calls these stages “turning points” and says each point exhibits changes in connectivity that could lead to a better understanding of what the brain is good at or vulnerable to in different seasons of life.

Throughout the childhood phase from birth to age nine, connections in the brain consolidate. The most active neuronal pathways grow stronger, while unused or weak connections are pruned. The next phase, adolescence, lasts until age 32, during which the brain’s communication networks are refined so information can move more quickly from one area to another. Mousley says this is the “only phase where the brain is becoming more efficient over time.”

After adolescence, connections begin to stabilize and efficiency decreases. Cognition and behavior are more consistent in the adult phase from age 32 to 66, but the brain’s networks begin to reorganize gradually during early aging, from about age 66 to age 83. By the time a person reaches late aging, the pathways in their brain have consolidated into specific regions that are more connected to themselves than to each other.

“So, there’s kind of this grouping thing where connectivity across the whole brain is weakening and there [are] these strong groups forming,” Mousley explains. “There [are] these hubs that are needed for lots of different paths.” Just as more airplanes pass through large central airports than smaller rural locations, the brain uses more of these hubs and fewer whole-brain connections to process information in late aging.

Even though past research has shown that the brain is “constantly rewiring,” Mousley isn’t aware of any previous work that gave a clear explanation of broad age-correlated patterns. Finding these patterns in the brain’s wiring took a lot of work, and Mousley says it wouldn’t have been possible without her supervisor’s willingness to let her “dig into the data set and be creative with it.”

“Obviously I’m looking at over 4,000 brain scans, and so the time it took me to gather that together, to organize it, to set it all up—it was a long process.” That freedom to explore allowed Mousley to look at brain development in fresh ways that helped her pinpoint changes in connectivity.

The novel discoveries are earning Mousley and her team’s paper widespread recognition. The research has been featured in outlets like the BBC, the New York Times, National Geographic, Scientific American, and the Washington Post. The outpouring of interest surprised Mousley because researching the paper felt normal to her. Even her supervisor, Duncan Astle, Program Leader at Cambridge’s MRC Cognition and Brain Sciences Unit, didn’t realize the research would get so much attention.

“He said something like, ‘Let’s just make a press release and see what happens,’” Mousley recalls.

While she’s happy that people are excited about her work, Mousley is quick to emphasize that the age ranges are averages based on broad, general patterns, not definitive numbers that apply to every person. She and her team also didn’t evaluate other factors like behavior or cognition; they only looked at the brain.

Still, Mousley hopes that understanding these changes in connectivity across the human lifespan could help predict problems with cognition and brain health, particularly the risk of developing mental health disorders in adolescence or dementia in early aging. She says the potential for future work in these areas is what excites her most about the project.

Mousley’s passion for neuroscience was clear during her time at Vassar. Over the course of two years working in Professor Hadley Bergstrom’s memory neuroscience lab, she played an instrumental role in several projects and co-authored three papers, which Bergstrom says is rare at other undergraduate institutions.

He recalled that “Alexa was just an outstanding, exceptional student. It’s amazing to be able to interact with all these talented students and to potentially have some kind of role or impact, however small it may be. It’s so rewarding for me.”

Mousley says her work with Bergstrom was fundamental to her understanding of science. “I owe Vassar so much. Really, the foundation of all my neuroscience experience, and also excitement, came from those experiences at Vassar.” —Theresa Houghton