Riddle me this: how can it be that reading these words activates nearly identical word-sensitive patches of the brain's visual system in you and nearly every other reader of this story? And that a different set of face-sensitive visual regions—again in almost identical positions in each reader's brain—would activate to process the faces of the researchers, should you meet them?
For years, researchers have debated how our brains consistently develop areas specialized for recognizing faces, objects, words, and places, despite individuals having vastly different life experiences.
Two competing theories have dominated this discussion. One proposes that these specialized brain regions are fully "hard-wired" from birth, predetermined by our genetic code. The other suggests that the brain begins as a "blank slate," with specialization emerging entirely through experience and environmental input.
Now, a groundbreaking study from researchers at Stanford's Wu Tsai Neurosciences Institute and international collaborators offers a nuanced perspective that bridges these two extremes.
The research emerged from the laboratory of Kalanit Grill-Spector , the Susan S. and William H. Hindle Professor in the School of Humanities and Sciences and a Wu Tsai Neurosciences Institute affiliate, and was led by psychology graduate student Emily Kubota , an alum of Wu Tsai Neuro's Mind, Brain, Computation and Technology program. The findings, published March 17 in Nature Human Behaviour , reveal that while key aspects of brain organization are present from birth, there's also significant capacity for flexibility and development through experience.
"I was really curious about the idea that some things about humans are already set from birth, and then the environment and experience can change quite a lot as we develop," Kubota explained. "I really wanted to know what is set from birth and what has the capacity to change."
The research focused on the ventral temporal cortex (VTC), a brain region crucial for visual recognition of objects, faces, words, and places. Previous studies in adults have shown that these category-selective areas are consistently located in similar parts of the brain across individuals. This consistency has led to debates about whether these regions are innately specified or shaped entirely by experience.
To investigate this question, the researchers needed to examine infant brains—a challenging feat that had not previously been feasible with traditional MRI brain imaging approaches. But this is an area where Grill-Spector's lab has been innovating for many years, including as a lead participant in the NeuroDevelopment Initiative at Wu Tsai Neuro, supported by one of the Institute's flagship Big Ideas in Neuroscience grants.
"With the help of Wu Tsai Neuro, we got funding to build baby-specific MRI coils," Grill-Spector explained, referring to the core components of an MRI scanner that serve as antennas for exciting and detecting subtle magnetic changes to map brain structure. As a result of a productive collaboration with co-author Boris Keil , a world expert in MRI coil design at the University of Applied Sciences Mittelhessen in Giessen, Germany, Grill-Spector said, "we now have coils for infants from birth to one year and one to two years, which lets us image the brains of babies of different sizes, as baby brains actually grow a lot in the first year."
Using these custom coils—as well as software tools to adapt to differences in infant brain structure—the team mapped patterns of connectivity in the brains of sleeping infants from birth to six months of age, as well as adult brains for comparison. This required advanced diffusion MRI (dMRI) techniques, which can trace bundles of nerve fibers—the brain's white matter—linking different brain regions.
The team was also faced with the problem of how to find—much less study—the infant versions of brain areas known to be involved in recognizing different categories of visual input in adults. To do this, the team essentially created a digital time machine to project the location of adult functional regions backward onto infant brains using brain anatomy as a guide.
The results revealed a surprising level of organization in infant brains. The researchers found that regions in VTC with distinct cellular organization, or cytoarchitecture, also had distinct white matter connections from birth. They also found that connections were organized based on whether they were carrying visual information originating from the center or periphery of the visual field (termed visual "eccentricity"). Specifically, VTC regions destined to become face and word areas started out from birth with more connections carrying high-resolution details from the center of the visual field, while regions destined to become place-sensitive areas started off with more connections to peripheral visual regions.
This organization remained stable through development into adulthood, and could help explain how common functional areas develop in a consistent way across individuals without actually needing to be hardwired from birth, the authors said.
Kubota sees the results as "an optimistic story," she said, "because it suggests that you have this underlying neural architecture from birth that can be used to build the ability to recognize different categories, but it's not so tied to the category itself. It means there can be some kind of flexibility as these representations emerge."
While the overall organization was stable, the researchers also observed changes in the strength of connections to different brain regions over time, suggesting that white matter connections are far from set at birth. Interestingly, they found that connectivity profiles of functional regions within VTC areas sharing the same cellular architecture developed in parallel, suggesting a shared developmental trajectory. Together, these findings show that white matter connections have both innate organization and the capacity to change over development.
"This insight is only possible because we've been able to measure the white matter of specific functional regions at birth for the first time," emphasized Grill-Spector, who is. "I'd like to think our research can shift the discussion away from the dichotomous 'Is this innate or not innate' kind of conversation to a more nuanced understanding of what is present at birth and what is malleable with visual experience to produce our adult brains and behavior."
The study's implications extend beyond just understanding normal brain development. By identifying which aspects of brain organization are present at birth and which develop through experience, the research could inform early identification of atypical white matter development, potentially leading to earlier diagnosis and intervention for developmental disorders such as dyslexia, developmental face blindness (prosopagnosia) and autism, to name a few.
"It tells us about the limits of the flexibility of our visual system, and also has health implications about how to diagnose developmental delays or deficiencies, and maybe what would be the critical time periods that you might want to intervene," Grill-Spector said.
Looking ahead, the researchers plan to continue studying brain development in infants, incorporating additional measures such as functional brain activity and quantitative MRI to gain a more comprehensive understanding of how the brain develops in early life.
This research represents a significant step forward in unraveling the complex interplay between innate brain structure and experience-dependent development. By showing that the brain has innate organizing principles that guide but do not rigidly determine its functional architecture, the study offers a more nuanced perspective on the age-old nature versus nurture debate.
Publication Details
Research Team
Study authors were Emily Kubota, Sarah Tung, Christina Tyagi, Sophie Duhameau, Danya Ortiz, Vaidehi S. Natu, and Kalanit Grill-Spector of the Stanford Department of Psychology and Wu Tsai Neurosciences Institute; Xiaoqian Yan of Fudan University in Shanghai; Bella Fascendini of Princeton University; Mareike Grotheer of Philipps-Universität Marburg in Germany; and Boris Keil of TH Mittelhessen University of Applied Sciences in Germany.
