What's it like to be a baby? Scanning their brains can help us find out

Anyone who has tried to entertain a baby knows sitting in stillness and silence is probably not the best way to keep them engaged, which presents a challenge for neuroscientists who want to study the developing brain.

Yet with the help of some TV, attentive parents and a lot of patience, researchers have designed protocols that help them keep babies awake and still in an fMRI machine. Doing so is important: Getting a clear reading on these brain scans can reveal never-before-seen details about what parts of the brain are active at a young age, helping researchers answer questions about memory, perception and cognition.

“The goal of this research is to try to understand the human mind, and a really valuable perspective on that question is understanding how it develops,” said Dr. Nick Turk-Browne, a psychology professor at Yale University studying infant cognition. 

Scientists are still discovering new parts of the brain, and what happens in the developing mind has historically been hard to pin down in neuroscience research. Most information we know about the infant brain has traditionally been based on behavioral measures of where babies look or what they reach for in experiments. Other data extrapolates from animal experiments or cases in which people have undergone brain damage to infer what is happening in functional brain regions. 

However, using an fMRI machine is considered the gold standard for mapping brain function, said Dr. Tristan Yates, a cognitive neuroscientist at Columbia University who studies perception and memory in early life.

“The reason why is it gives you whole brain coverage … including access to really deep brain regions,” Yates told Salon in a phone interview. This technology gives researchers access to more detailed information about certain brain regions that could answer some major questions about cognition, she added.

When fMRI machines came online in the 1990s, researchers did use them to look at infant brains, but these scans were typically conducted when babies were sleeping, Yates said. This means they couldn’t study how aspects of the waking brain like cognition were impacted by various stimuli.

But in 2002, a research team in France successfully captured fMRI images of awake infants to measure how their brains responded to language. Another research team in Italy performed a similar experiment in 2015, and the first study scanning the brains of awake babies in the U.S. was published in 2017. In the near-decade since, various research teams have begun to explore what is going on in the infant mind to better understand neural development.

“This fMRI work is also in its infancy, and it’s only really a handful of labs around the world that are doing it,” Yates said. “We’re excited that we’re going to be able to start to disentangle what is going on here.”

At birth, a baby’s brain is roughly one-third the size of an adult brain. It nearly doubles in size in the first year of life, making millions of neural connections each second in an endless process of learning. 

Still, an infant brain’s relatively small size doesn’t mean that it is necessarily underdeveloped: Surprisingly, fMRIs have shown that baby brains in many ways remarkably resemble adult brains, said Dr. Cameron Ellis, a psychology professor at Stanford University who researches what it’s like to be an infant.

“When I started this work over 10 years ago … I expected it to be an alien landscape where many of the assumptions that we had and many of the things that are true about the adult brain wouldn’t apply,” Ellis told Salon in a phone interview. “I have been proven wrong time and time again: Actually, the infant brain looks a lot like the adult brain.”

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Although baby fMRIs have been helpful in highlighting what regions of the brain are operating in infancy, one limitation with this data is that activity in certain brain regions does not necessarily translate to the same thing in infants as it does in adults, Ellis noted.

“It’s something we have to be careful in this field of not over-interpreting similarity between infants and adults as meaning something about their cognitive capacity in its own self,” Ellis said.

Nevertheless, this research has changed the way researchers think about the developing mind in many ways. For example, neuroscientists often have the intuition that earlier in development, the infant experience is limited to more sensory processes like vision, hearing and touch, but that things that require one to attribute meaning or connect two things occur later in development, said Dr. Rebecca Saxe, a professor of brain and cognitive sciences at the Massachusetts Institute of Technology.

However, in a study Saxe authored last month in the journal Current Directions in Psychological Science, she and her colleagues found something that challenges previous assumptions about how infant brains develop. Specifically, the areas of the medial prefrontal cortex responsible for processing social environments were active when infants were exposed to faces. In adults, this region is also active with ideas of the self, like when you see your own phone number versus a random phone number, Saxe explained.

“Maybe it’s not that first babies do visual processing and only later are connected to social meaning,” Saxe told Salon in a phone interview. “Maybe these brain regions are active because babies are responding to the social meaning of people and faces as early on as we can measure their brains.”

In one study Turk-Browne, Ellis and Yates authored in Neuron in 2021, fMRI data showed activity in infants’ visual cortex when presented with different visual cues, indicating that babies are able to map out the world in front of them in their minds in a process called retinotopy as early as five months old. This is impressive that their process so closely resembles the adult brain’s considering a baby’s vision is still developing in the first few months of life.

In another study, a research team found that parts of infants’ brains in charge of shifting attention in the frontal parietal cortex were activated in infants as young as three months old. 

“What’s surprising about that is these are some of the parts of the brain that are thought to be the slowest to develop,” Turk-Browne told Salon in a phone interview. “You’ve probably heard about this idea that our frontal lobe continues developing through adolescence, and that’s true, but what we were showing is that some of the more rudimentary kinds of things like how we shift our attention and control our minds may be supported by those brain regions even in infancy.”

However, there are important differences between infant and adult brains. In one 2022 study published by Turk-Browne, Ellis and Yates, infants were shown to process events on longer time scales than adults. This could be an important learning tool to help infants absorb more information about their environment before making a judgment about it based on their past experience, Yates said. 

For example, infants can distinguish between sounds made in various languages at birth, but at around six to 12 months, they start to narrow in on the language they are around most often and lose the ability to distinguish between sounds made in other languages. 

“We haven't related this to learning yet, but it makes sense that it might be helpful to start kind of a big picture and then narrow it down,” Yates said. “One thing that happens in infancy is this process of perceptual narrowing, where babies in some ways have broader perceptual abilities than adults.”

There also seems to be a difference in processing memories in infancy and adulthood. After all, people don’t remember their infancy, with the first memories typically reported around the age of three or four. 

The hippocampus is the brain structure responsible for memory, and it helps us remember specific memories of events that occurred at a certain time and place, as well as a more general sense of memory called statistical learning, where the brain detects patterns in the environment. For example, as children start going to different kinds of restaurants, statistical learning helps them understand what kinds of foods are served at a Mexican restaurant, a Thai restaurant and so on.

Infants have been shown to be good statistical learners. After all, that’s how they pick up language, learn to recognize their family members and begin to understand the subtleties of their cultures. But it wasn’t clear if this type of memory also happened in the hippocampus in infants, especially because the hippocampus doubles in size across infancy.

To investigate this question, the research team showed infants a series of random and structured images while they were hooked up to the fMRI machine to see whether these areas of the brain were active when infants remembered the structured images over time. What they found was that these same regions of the brain were indeed active in infants as young as three-months old. 

“That’s a surprising finding because the alternative was that maybe in infants, the rest of the brain, or another part of the brain, is important for that kind of learning,” Turk-Browne said. “But in fact, we found that the adult mechanisms for statistical learning may be functional in babies.”

This finding didn’t explain why we can’t remember being babies, but it did help researchers narrow down what questions they needed to ask to find out. Memories were activating the same regions in the brain in infants as they were in adults, but it could be that these memories cannot be stored in infancy. Or, it could be that the memories are stored in infancy but that they become inaccessible to us later on in life.

In another study, published in March in Science, the research team studied the hippocampus of infants hooked up to an fMRI machine was able to store specific episodic memories — not just statistical patterns — as early as 12 months of age. This suggests that the reason we don’t remember our earliest years is related to how they are encoded in the brain.

“There may be some of our early memories present in our brain, at least for some of our life, despite the fact that we can’t access them,” Turk-Browne said. 

Turk-Browne’s research lab is currently conducting studies to better understand how long those memories last in an infant’s mind and how detailed they are. This could help explain the disconnect between how we experience memories as infants and as adults.

What they find could help prove or disprove several theories on why we don’t remember being babies. It could be, for example, that the way infants experience the world is different before they learn how to talk, and that labeling things with words and language helps shape our memories with more longevity. 

For example, a six-month old child may remember being at a birthday party and hearing their family members talking, but if they can’t make sense of the words and haven’t yet learned about birthdays, they might not sort this memory with the kind of detail that their older self would use to recollect it later on.

“It’s like the memory is there, but you don’t know how to find it, like an indexing problem,” Ellis said. “It’s as if you went to the library and then someone changed all of the numbers so the book are not where they used to be.”

Nevertheless, understanding why could help us better understand how things like early childhood experiences can be so influential later in life, even if they cannot be explicitly recalled, Yates said. It could also help us better understand how memory conditions like dementia or Alzheimer’s develop, Ellis said.

“For patients with Alzheimer’s, the breakdown that might be happening in their brain could perhaps be repaired by implementing some of the changes that the infant brain goes through as it acquires learning and memory,” Ellie said. “It’s entirely speculative at this point because we don’t know what those changes are, but that is a potential hope in the future.”