What Babies Know About Their Bodies and Themselves
Article by Perri Klass, M.D., first appeared in the The New York Times, July 2018
We are accustomed to thinking about the importance of what even very young babies see and hear, but “touch is the first sensory system to develop in the baby’s brain prenatally,” and is quite well developed by the time the baby is born, said Andrew Meltzoff, the co-director of the Institute for Learning and Brain Sciences at the University of Washington.
Dr. Meltzoff was the first author on a study published in late June in the journal Developmental Science, which looked at how 60-day-old infants’ brains responded when different parts of the body were gently tapped.
“We know relatively little about how the infant brain responds to touch,” Peter J. Marshall, chairman of the department of psychology at Temple University, and another author on the study, said in an email. “There is a lot of research on ‘body maps’ that respond to touch in the adult brain, but very little work on how those maps develop.”
The researchers put stretch caps containing EEG electrodes on the babies. These sensors, which are painless for the babies, record brain activity.
“There was a neural signature, a spatial distribution of electrical activity in the EEG that helped show us what part of the brain was active,” Dr. Meltzoff said. When the left hand or foot was touched, they saw activity in the right side of the brain, as they expected; in an area closer to the center for the foot, and further to the side for the hand; when the upper lip was touched, the activity was bilateral.
“Not only does this touch produce a robust and measurable response in the brain, but that response is extremely organized,” said Dr. Joni Saby, the other author. “The strongest response is to the lips, which is interesting because babies this age spend most of their time eating, sucking.”
The way the body is represented in the brain is called neural mapping. For the adult body and the adult brain, for example, it has been shown that the motor and sensory nerves to the foot map to the central part of the brain and the walls between the hemispheres, while the hands map further out to the sides. This is sometimes represented by a drawing of what has been called the homunculus, a collection of human body parts ranged along the sections of the adult brain, proportioned according to their sensory and motor importance.
Dr. Meltzoff said that in a phenomenon called “cortical magnification,” the lips may be “overrepresented, there’s more neural tissue devoted to the baby’s lips than to hands and feet.” The cortical magnification may reflect the feeding the babies have already done, he said, but “it’s perfectly possible that for evolutionary reasons, baby humans have a very prominent lip representation because lips are used not only for survival but for emotional expressions and language.”
And the hands are going to be used to explore the world — these babies are still too young to be intentionally reaching and grabbing, but the hand is already well represented in the brain, which may be a precursor to the reaching behavior soon to develop.
In another study published earlier in 2018, 7-month-old babies were shown a film of somebody else’s hand being touched, and the hand areas of their brains became active. “Babies as young as 7 months are able to connect self and other,” Dr. Meltzoff said, and speculated on the implications of the baby understanding, “their hand is like your hand, their lips are like your lips; I am like you, you are like me.” This process in which the baby looks out at another person’s body and sees it as being “like me,” he said, could be an important foundation for social and cognitive development.
“Before humans have language, they have the language of touch, they communicate through the language of touch,” Dr. Meltzoff said. Parents understand the importance of skin-to-skin contact with babies, he said, and recognize both that it can calm the baby, and that it can be very rewarding for the parent. “There’s something like a touch hunger in young babies,” he said. And from touch comes important developmental stimulation, including a sense of the baby’s own body.
Dr. Saby, who is a postdoctoral fellow in radiology at the Children’s Hospital of Philadelphia, said she has been studying babies in the research lab for 10 years, but now with a 5-month-old of her own, “I’m finally seeing everything through the parent’s eyes.”
She finds herself feeding her baby, “thinking about every time I touch her hand, there’s activity sent to that part of her brain that represents her hand,” she said. “Constant stimulation going to her brain helping develop that area, helping their brains connect with their bodies, and eventually they’re going to be able to use those body parts for other things, not only motor things, but helping to understand other people’s body parts as well.”
“Prior to language, a lot of social emotional interaction comes through touch,” Dr. Meltzoff said, and understanding this representation of the body may help explain the groundwork for social emotional development. “If you ask me to speculate, I would say the baby has a very primitive sense of self in the first months of life. It may be primarily a tactile kinesthetic sense of self,” that is, a sense of self related to touch and to body movement.
For young babies, Dr. Meltzoff added, “touch tells them about themselves when they’re in the bassinet alone, touching their face, shaking their hands.” When they’re kicking their feet, or opening and closing their hands, he said, and those associated brain regions are active, you could think of it as a kind of “body babbling.”
“This is me, I can touch my lips,” he said. “It’s a preverbal body exploration.”
Next steps would be to map out different body parts more completely in the baby brain, and then look closely at how the behavior patterns affect the brain as the baby develops. Does the neural representation of the feet change and expand as the baby begins to walk? As they begin to use their hands more to reach and grab more deliberately, does the hand representation increase and become more finely detailed?
“A baby has a representation of their own body and uses that representation of their own body to process information about other peoples’ bodies — that’s a theoretical statement,” said Dr. Meltzoff. “If that’s true, if the baby’s neural representation of self is used to map self and other, it launches the big bag of social communication.” It might help answer the question of why babies, right from birth, focus their attention on people rather than objects that they see.
“We think this research shows they have a bodily sense of self,” Dr. Meltzoff said. And that in turn raises intriguing questions about the origins of self-consciousness, and the development of connections between the self and others that make us the social creatures that we are. Looking at baby behavior and at how brain and behavior are interconnected in infant neuroscience may thus take us close to essential philosophical questions about what makes us who and what we are.