I recently found myself in a touch tunnel at a science museum. Basically in pitch darkness in a box, I had to feel my way through a maze of turns. As I did so, I found myself often thinking about my arms’ position relative to not just the tunnel but to each other and the rest of my body.
This is something we do everyday, usually unnoticed, whether swatting at a mosquito on your arm or even when typing on different keyboards. This process of tracking our limbs’ movements in space is called body mapping. And in a new paper, researchers report on recent studies that find we start creating body maps as early as infancy, which eventually enables us to connect with other people.
“Body maps are the result of an organized mapping between the neurons that carry signals to and from parts of the body and the areas of the brain that process these signals,” says Peter Marshall of Temple University. This constant mapping of the body in space is well known from studies of “phantom limb syndrome,” he says.
Referring to the work of V.S. Ramachandran, he explains how in some patients who had lost an arm, their brains rewired their body maps “in a very striking way. If the person was touched on the cheek, he or she might experience the sensation of being touched on the missing hand.” Researchers think that because the “face area” is next to the “hand area” in somatosensory cortex, when the normal input to the hand area was lost, the pattern of connectivity within the body map was reconfigured.
Marshall says that body maps in adults can be altered by other kinds of experience as well: “A famous study by Thomas Elbert and colleagues showed that the size of the representation of the fingers of the left hand in expert string instrument players is related to how long they had been playing the instrument.” Yet despite these studies and others in adults, neuroscientists have not known much about how body maps develop in the human brain.
Teaming up with Andrew Meltzoff of the Institute for Learning and Brain Sciences (I-LABS) at the University of Washington, as well as former grad student Joni Saby who is now at I-LABS, Marshall has been exploring how infants come to develop a basic sense of self and how that enables them to develop connections with other people. “The research on body maps came out of these questions,” he explains.
In the recent Trends in Cognitive Sciences paper, the researchers discuss the implications of two studies. In one study published in PLOS One, the researchers found that when infants watched someone else carry out an action with his or her hand, they could measure activity in the part of the infant brain that processes information from the hand. When the infants watched someone carry out an action with his or her foot, they could similarly observe activity in the foot area of the brain. “This suggested to us that body maps might be important in connecting self and other and that they may allow infants to imitate the actions of other people, which is an important mechanism for learning about people and actions,” Marshall says.
In another study, published in Neuroimage, the researchers developed a way to send mild tactile stimuli to infants’ hands and feet while recording electrical brain activity using a stretchy EEG hat. They found that the brain responses to tactile stimulation of infants’ hands and feet are, like adults, organized in a “somatotopic fashion” – with different body parts mapping to a corresponding point on the primary somatosensory cortex. “We also spent a lot of time fine-tuning the methods for presenting tactile stimulation to infants, so it was good to see that these methods produced robust brain responses,” he says.
The hope, Marshall says, is that the research on body maps will help tell us how infants develop a basic sense of themselves, even in the early weeks of life. “In turn, we are interested in how that sense of self might allow infants to form the earliest social connections.” Also, although speculative, understanding the role of body maps in connecting the self to others in early development might have implications for the study of autism spectrum disorder (ASD).
“The work on body maps in the infant brain is only just beginning, and at this point we still don’t know much about the typical development of these maps and how they relate to the changing social and behavioral capacities of infants,” Marshall says. “While there are some interesting future directions to explore in terms of body maps and atypical development, at this point we really don’t know if body maps might have different properties in children with developmental disorders such as ASD.”
-Lisa M.P. Munoz