Developing our sense of touch

How do we end up with a somatosensory system in the first place? Georgia Mills spoke to Marie Curie Research Fellow Stephanie Koch from UCL, who studies how the somatosensory system develops in babies. First, Georgia asked, when are babies first capable of sensing touch?

Stephanie - We’re starting to get an idea of this. But to put this into context, it’s really important to remember that infants, unlike adults, can’t tell us when they’re experiencing touch or pain, so researchers and scientists really have to rely on behavioural cues and how they respond. And those are all spinal circuits, essentially looking at spinal circuitry, and when we look at that we can see that as soon as an infant is born, they start to respond to touch and pain and what changes over development is their sensitivity to touch and their sensitivity to pain. So infants are very sensitive to touch and to pain and we gradually become less so with age.

Georgia - I’ve noticed, stinging nettles always used to hurt a lot more when I was little. Do we know how these systems do develop?

Stephanie - We were getting an idea of it. It’s really interesting that both touch and pain learn from experience, these somatosensory systems, like vision, like the auditory system. But, in a very unique way, they don’t learn from their own sensory modality so it seems like touch is actually learning from spontaneous movements like muscle twitches, for example, and pain is learning through the experience of touch. And that’s really interesting because biology has evolved to allow us to learn what pain is without having to have the infant go through all these potentially harmful experiences.

Georgia - Wow! That would seem quite counterintuitive. You’d expect that pain teaches more pain.

Stephanie - Right, exactly.

Georgia - So how do babies rely on touch to develop normally?

Stephanie - A lot of what we’ve seen in both clinical studies and in animal studies is that skin to skin contact is really crucial for the normal development of infants as well as animals, long term and short term. We know that these touch circuits are really critical for the normal maturation of pain in general, and that’s touch that’s passive through movements as well as touch that’s active in terms of interactions, for example. And that touch allows pain circuits to be formed both physiologically and biologically so that as adults we can recognise what a painful stimulus is and avoid it reflexively and protect ourselves.

Georgia - And that’s quite important so we don’t all end up burning our fingers off and things like that. Has anyone ever done the study to find out what happens if you’re deprived of touch completely?

Stephanie - We obviously can’t really do that with infants, with humans. So most of the studies that have been done looking at this is with animal studies, and if you deprive them entirely of touch then you stunt pain development. Even when the animals grow up they feel pain as if they were newborn, so their thresholds to pain are very low and their sensitivity to touch is very high, and that shows us how important touch is for the development of a pain circuit in itself.

Georgia - So that’s deprivation. What about if an infant did have a painful experience; for example premature babies might have to undergo surgeries or something like that, do we know what that does?

Stephanie - We’re starting to have more of an idea of that. We’ve really been talking about how experience is necessary for the building of a touch and a pain later experience in life and how we’re going to build our thresholds. So normally, whereas you and I will be able to have that key setting that will allow us to experience the world as we would otherwise. In some instances as your saying, like premature infants, they’re going to have repeated surgical interventions throughout their lives and that means that their somatosensory experience is altered. Studies that have followed these infants have shown that they have an altered pain threshold for the rest of their lives and, in some cases, these infants have higher pain thresholds and some instances they are lower pain thresholds. We don’t fully understand the implications of this but it’s an area of active research and it’s very important to look into.

Georgia - Right. What about birth itself because obviously we always talk about how painful birth is for mothers, what about the baby?

Stephanie - I think this is very interesting as a concept. We don’t fully know, and I’m not really sure how we’d look into it. But it’s clear that birth itself is a sensory experience for the child and I think what we’re looking at is how the infant is brought into the world and how that can perhaps prime them to be able to react with their surroundings later on.