A key region of the brain’s visual cortex responds to faces the same way in infants and adults

MIT researchers have discovered regions of the infant’s visual cortex that show strong preferences for faces, bodies, or scenes, just like in adults. Credit: MIT News, With images courtesy of Researchers and iStockphoto

One study suggests that this area of ​​the visual cortex appears much earlier in development than previously thought.

In the visual cortex of the adult brain, a small region is specialized to respond to faces, while neighboring regions show strong preferences for bodies or for scenes such as landscapes.

Neuroscientists have long hypothesized that it takes many years of visual experience for these areas to develop in children. However, a new MIT The study suggests that these regions form much earlier than previously thought. In a study of babies aged two to nine months, researchers identified areas of the infant’s visual cortex that already show strong preferences for faces, bodies, or scenes, just like in adults.

“This data improves our picture of development, making babies ‘brains more like adults’ brains in more ways and sooner than we thought,” said Rebecca Saxe, John W. Jarve science professor. of Brain and Cognition, member of MIT. McGovern Institute for Brain Research, and lead author of the new study.

Using functional magnetic resonance imaging (fMRI), the researchers collected usable data on more than 50 infants, a number far higher than any research lab has been able to digitize before. This allowed them to examine the infant’s visual cortex in a way that had not been possible until now.

“This is a finding that will force a lot of people to really grapple with their understanding of the infant brain, the starting point of development and development itself,” says Heather Kosakowski, MIT graduate student and lead author of the study. published on November 15, 2021 in Current biology.

Distinctive regions

Over 20 years ago, Nancy Kanwisher, Walter A. Rosenblith Professor of Cognitive Neuroscience at MIT, used fMRI to discover the spindle-shaped area of ​​the face: a small region of the visual cortex that responds much more strongly to faces than anything else. other type of visual. grab.

Since then, Kanwisher and colleagues have also identified parts of the visual cortex that respond to bodies (the extrastriated body area, or EBA) and scenes (the parahippocampal area, or PPA).

“There is this set of functionally very distinct regions that are present in more or less the same place in virtually all adults,” says Kanwisher, who is also a member of the Center for Brains, Minds, and Machines at MIT and author of the new study. . “It raises all these questions about the development of these regions. How do they get there and how do you build a brain that is so similarly structured in each person? “

Dynamic stimuli

After entering the specialized scanner, along with a parent, the babies watched videos that showed faces, body parts such as kicking or waving hands, objects such as toys, or natural scenes such as mountains. This figure shows examples of images used in the study. Credit: Courtesy of the researchers

One way to try to answer these questions is to study when these highly selective regions first develop in the brain. A long-held assumption is that it takes several years of visual experience for these regions to gradually become selective for their specific targets. Scientists studying the visual cortex have found similar selectivity patterns in children as young as 4 or 5 years old, but there have been few studies in children younger than this.

In 2017, Saxe and one of its graduate students, Ben Deen, reported the first successful use of fMRI to study the brains of awake infants. This study, which included data on nine babies, suggested that while infants have areas that respond to faces and scenes, those areas were not yet very selective. For example, the fusiform facial area did not show a strong preference for human faces over any other type of entry, including human bodies or the faces of other animals.

However, this study was limited by the small number of subjects, as well as its reliance on an fMRI coil that the researchers had developed especially for babies, which did not offer imaging as high as resolution. the coils used for adults.

Heather Kosakowski

“This is a result that is going to force a lot of people to really grapple with their understanding of the infant brain, the starting point of development and development itself,” says Heather Kosakowski, pictured, MIT graduate student and principal author. of the study. Credit: Kris Brewer

For the new study, the researchers wanted to try and get better data, from more babies. They built a new scanner that is more comfortable for babies and also more powerful, with a resolution similar to that of fMRI scanners used to study the brains of adults.

After entering the specialized scanner, along with a parent, the babies watched videos that showed faces, body parts such as kicking or waving hands, objects such as toys, or natural scenes such as mountains.

Researchers recruited nearly 90 babies for the study, collected 52 usable fMRI data, half of which contributed to higher resolution data collected using the new coil. Their analysis revealed that specific regions of the infant’s visual cortex exhibit highly selective responses to faces, body parts, and natural scenes, in the same places where these responses are seen in the adult brain. The selectivity for natural scenes, however, was not as strong as it was for faces or body parts.

The infant’s brain

The results suggest that scientists’ design of how the infant’s brain develops may need to be revised to account for the observation that these specialized regions begin to resemble those of adults sooner than expected.

“What’s so exciting about this data is that it is revolutionizing the way we understand the infant brain,” says Kosakowski. “Many theories have emerged in the field of visual neuroscience to accommodate the idea that it takes years of development for these specialized regions to emerge. And what we’re saying is actually, no, you really only need a few months.

Because their data on which area of ​​the brain reacts to scenes was not as strong as for the other places they examined, the researchers now plan to pursue additional studies of that region, this time showing images of babies on a much larger screen that more closely mimic the experience of being in a scene. For this study, they plan to use near infrared spectroscopy (NIRS), a non-invasive imaging technique that does not require the participant to be inside a scanner.

“This will allow us to question whether young babies have robust responses to visual scenes that we underestimated in this study due to the visual constraints of the experimental scanner setup,” says Saxe.

The researchers are now further analyzing the data they collected for this study in hopes of learning more about how the development of the spindle-shaped area of ​​the face progresses from the youngest babies they studied to the oldest. They also hope to conduct new experiments examining other aspects of cognition, including how babies’ brains respond to language and music.

Reference: “Selective Responses to Faces, Scenes and Bodies in the Ventral Visual Pathway of Infants” by Heather L. Kosakowski, Michael A. Cohen, Atsushi Takahashi, Boris Keil, Nancy Kanwisher and Rebecca Saxe, November 15, 2021, Current biology.
DOI: 10.1016 / j.cub.2021.10.064

The research was funded by the National Science Foundation, the National Institutes of Health, the McGovern Institute, and the Center for Brains, Minds, and Machines.


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