These are my notes from reading Lise Elliot’s What’s Going On in There?.
“The Importance of Touch”.
This chapter goes through the development of the sense of touch, which is the first sense to emerge and the most advanced one at birth. It also covers the related senses of pain and temperature. Touching is shown to be immensely important for the normal development of a baby, with babies raised in isolation growing up stunted physically, mentally and emotionally (or dying in early age).
A few interesting facts I learned:
- Nerve signals for touch, temperature, pain and proprioception go along very similar, parallel pathways.
- Touch signals are mapped to a body map in the brain (which I knew). This map needs stimulation to develop: if it gets no signals from a certain part of the body, the corresponding neurons do not develop normally. In humans this development happens before the baby is born.
- The sense of touch is diffuse in babies. Over time that map of the body grows sharper and babies get better at distinguishing which part of the body they felt the touch on.
- Touch develops head to toe. The face is most sensitive to begin with, and remains more sensitive than the hands until the child is 5 years old.
- Babies (human and animal) need touch for their normal development. Babies who get adequate food and medical attention, but are not touched and held, grow up sick and stunted. Massage is beneficial for babies and children with all sorts of medical problems.
The elements of touch
The sense of touch covers four different abilities: touch itself (skin being in contact with something), temperature, pain and proprioception (sensing the position and movement of one’s own body). The first three use information from the skin; proprioception adds information from muscles and joints.
Touch signals start in touch receptors, which translate mechanical pressure into an electrical signal. The signal goes from the skin along the sensory neurons to the spinal cord and then to the brain stem. There the sensory neurons synapse on relay cells that cross over to the other side of the body, going on into the thalamus. In the thalamus the relay cells synapse with a third set of cells which go to the somatosensory cortex.
Temperature sensation travels along a similar pathway: to the spinal cord, where they cross over, then on to the thalamus and to the cortex. So the two sensations – touch and cold – may feel different, but they are transmitted in exactly the same way but along parallel pathways. The same is true for pain and proprioception.
The somatosensory map
There is a strip of somatosensory cortex on each side of the brain. Each one contains a mini-map of the body’s surface: adjacent body parts activate adjacent neurons. In fact each one only contains a map of half the body – the opposite half (right half in left brain and vice versa). And the map is significantly distorted, with more sensitive regions assigned a lot more space. A lot of this distortion is genetic: some body parts (like fingertips) have more sensory receptors, so they will outcompete other body parts for space in the brain.
But the establishment of body maps in the somatosensory cortex also depends on activity in the sensory fibers. Mice, for example, have very sensitive whiskers. Whisker sensation is necessary for proper development of the relevant brain structures: if a whisker row is removed before a critical point, the corresponding brain structures never develop. In humans this period corresponds to about the middle of gestation, implying that all the touch sensations that the fetus feels in the womb are crucial for establishing the sense of touch.
The perceptual maps continue to develop after birth, and touch experiences also contribute to the baby’s general cognitive development. Experiments with rat pups have shown that rats raised in an environment with lots of toys turn out cleverer (as long it’s not just the same old set of toys all the time, in which case the rats get bored and their brain cortex starts shrinking again). But luckily it’s not just toys that have this effect – the rats got a similar benefit if they were groomed by their mothers, or handled by the experimenters. The same probably goes for human babies.
Touch is the earliest sense to develop
The sense of touch is the first one to emerge, and is one of a baby’s most advanced abilities at birth, even if it is still far from fully developed. The regions devoted to touch and movement are really the only areas of the cortex to show any significant activity in a newborn brain. Therefore, if there is anything going on in there, it’s related to the baby’s awareness of touch.
The embryo can feel a touch to the nose or lips already five and a half weeks after conception. This extends to the rest of the face and the arms by the ninth week; by the twelfth week almost all of the body can feel touch. The only exceptions are the top and the back of the head, which may be helpful for the birth process.
Even though the fetus can feel touch, it doesn’t have a conscious perception of touch like an adult does. Its touch pathways only reach the spinal cord and the brain stem. Therefore, simple reactions governed by the spinal cord – like the reflex to withdraw a limb if it is touched – emerge first. Later, when the signals reach the brain stem, touch signals are integrated with other senses like balance. The final connections to the cortex emerge only in the third trimester.
After birth, the myelination of touch nerves continues, and touch signals become stronger and faster. By the age of 6, the signals are almost as fast as in an adult. They also become more precise: early on the signals overlap and the map is blurry. As the child grows, the map grows sharper and the child becomes more and more accurate at figuring out where on her body the touch was located.
Touch develops head to toe
Touch sensitivity develops in a head-to-toe sequence. The mouth is the first region to become sensitive, which is why babies use it to explore everything. Even at 5 years of age, children’s faces are more sensitive to touch than their hands.
Babies can detect different shapes with their mouths, and different textures. They can also recognise when they are shown an object that they have previously only felt in their mouth, which means that they can form an abstract idea of that object. Their hands are far less sensitive: if they get to hold an object in their hands, they will not be able to recognise it when they later see it.
But the hands are nevertheless busy. Even before birth, babies use their hands to touch all parts of their body, especially the face. At 10 weeks they can distinguish different shapes with their hands, and at 6 months, different textures. Only at 18 months can the distinguish objects that are only subtly different, such as a cube vs. a cube with a notch cut into it.
At birth, both hands are equally good (or bad) at recognising things. By the age of 2, the left hand is slightly better – and this remains true for most adults. We tend to use the right hemisphere (thus, the left hand) to process information about shapes and spatial properties. The right hemisphere doesn’t specialise in this until after the first birthday – perhaps because this is when the left hemisphere becomes heavily specialised in language.
Babies feel pain already before birth
The sense of pain probably emerges before the third trimester of pregnancy: if they are not sedated, fetuses attempt to move away from the needle when a biopsy or a blood transfusion is performed. After birth, babies react to pain by intense crying, grimaces, body posture and physiological stress (stress hormones).
Due to these visible reactions it has always been known that babies react strongly to painful stimuli. Nevertheless it was long believed that they didn’t really feel the pain because the cerebral cortex wasn’t sufficiently developed. Because of this, and because of concerns about the safety of certain drugs, doctors would perform all kinds of procedures (including surgery) on newborns without any anesthesia. That is no longer the case now that we know that the somatosensory cortex begins functiong before birth.
There is some evidence that newborns become more sensitive to pain over the first few days. They could initially be less sensitive because of anesthesia that the mother receives, or because of natural pain-killing hormones that the baby’s body may produce to cope with being born.
Apart from that, babies’ sensitivity to pain does not chagne much over the first year. The nerves carrying pain signals have little or no myelin, so the nerves do not need myelination in order to reach their full potential. However babies’ pain signals will become more precise in terms of location, just as with the sense of touch, as the body map in the brain becomes sharp.
As in adults, pain experience in babies can be strongly affected by other stimuli. They react more strongly to pain when they are hungry, alert or fatigued, and less when they are distracted or sleeping. Sucking on breast or dummy, holding, swaddling, rocking, stroking etc can all reduce babies’ reaction to pain, as these stimuli interfere with pain signals.
While babies can feel pain, they do not have the psychological component of pain, the knowledge that they are suffering. Adults are able to remember painful experiences, but cannot recreate the actual feeling of pain. Babies lack conscious memory so they will not even be able to remember that they hurt. This is probably why many painful procedures (circumcision, piercing of the ears) is performed so early in most cultures. Babies also don’t anticipate pain – only in the 2nd year will they cry at the sight of an immunization needle.
But even if they have no conscious memory of pain (or anything else), babies are likely to be affected by early painful experiences. While babies don’t form conscious memories, they are capable of other forms of learning from early on: they can recognise people, associate one thing with another, and learn motor skills, after all. Early pain may prime the brain to be more sensitive to pain later.
Babies can tell the difference between a warm and a cold touch to the cheek as soon as they are born: a warm touch triggers the rooting reflex, while a cold one makes the baby turn away. Babies also pull away their hands from very hot or cold objects. By six months they can tell apart two identical objects where one is warm and one is cool (they become bored with the warm one and are more interested in the cool one).
This would seem to be an instinctive, unlearned skill. But observations of two “wild” children, who have grown up with no contact with other people, showed that they didn’t seem to feel hot or cold. One was reported to pull potatoes out of a fire with bare hands, and the other was completely unaware when she was not dressed for the weather. This suggests that physical sensation is not all – as with pain, there is a strong cognitive component.
Even though babies can feel temperature differences, they cannot do much about them, and cannot compensate for temperature extremes. They have less body fat than adults, higher surface-to-volume ratio, no ability to shiver and little ability to sweat. Their main way of responding is to change their activity level. When it is too hot, they slow down, sleep more and spread out their arms and legs to dissipate heat. When it’s cool, they wake up and move more to generate heat.
The benefits of early touch
Touch is important not only for sensory and motor development, but also for babies’ emotional and cognitive development, as well as for their overall health. This was first shown in a classical experiment with rhesus monkeys. Baby monkeys were given two fake “mothers” – one had a wire body but provided milk, while the other was covered with soft cloth but gave no milk. The monkeys visited the wire “mother” when they wanted milk, but spent the rest of the time with the cloth “mother”. It is touch and bodily contact that bond babies to mothers, not the fact that mothers provide food.
In other experiments, baby monkeys were brought up without a mother, but in groups of peers. These monkeys grew up more timid than monkeys with a normal childhood, but far more well-adjusted than monkeys growing up in isolation. But if they were prevented from touching one another (even though they could see, hear and smell each other) they did not get the same emotional benefits.
For many species early contact comes in the form of licking. Dogs, cats, sheeps and horses all lick their young after birth. This licking is so important that newborn animals often die without it – usually from a failure of the urinary or digestive tract. However if the mother is not present, a newborn (domestic) animal can get a similar effect from being rubbed down by a veterinarian.
Bodily contact also helps the nervous system cope with stress. Rat pups who are licked and groomed more, have a better-adjusted stress system: they are less fearful in novel situations, and their stress hormones peak at a lower level and decline faster.
If rat pups or baby monkeys are separated from their mothers, this leads to a suppressed immune system as well as lower growth. The effects can be seen years later. If the young animal is reunited with its mother within a short time (10 days in monkeys), the effects are reversed. The negative effects can also be prevented if the infant animal is stroked by human, again suggesting that it is touch and not warmth or nursing that is important.
Touch as treatment
Children who have grown up in isolation have been extremely emotionally disturbed. Even less extreme isolation is harmful. In the 1940s René Spitz compared two groups of babies. One group was raised in foundling homes, the other in a prison nursery.
The babies in the foundling home got adequate food and medical care but only minimal sensory and social stimulation. There was a single nurse for every 8 infants. Except for feeding and nappy changes, each baby was isolated in their crib. With nothing to play with and a minimum of human contact, they grew up stunted in every sense. Many didn’t even survive to two years of age. Those who did were physically stunted, prone to infection and severely retarded. By three years most couldn’t walk or talk, and were strikingly apathetic.
The babies in the prison nursery were cared for by their own mothers. Despite the institutional setting, and even though the hours of contact between mother and baby were limited, these babies developed normally.
Early adoption is now recognized as the best option for orphans and unwanted babies. When neglected babies are hospitalised, it’s often tender care and human contact that best promotes their growth and development.
One important group of babies for whom lack of touch has long been the norm is prematurely-born babies. They are often hooked to ventilators and feeding tubes, and many intensive care units have a “minimal touch” policy to avoid overstimulating these fragile babies. However recent research has suggested that they may gain more from gentle touch and contact. Instead of lying flat in roomy incubators, pre-term babies are now in more protected, nest-like environments, supported on all sides by soft cloth. Whereas previously parents were kept away from their babies because of fears about injury or infection, they are now encouraged to spend time holding their babies, preferably upright and skin-to-skin (“kangaroo care”). Both these changes help babies gain weight faster, sleep and breathe better and cry less.
Another way to provide pre-term babies with more touch is daily gentle massage. And pre-term babies are not the only ones to benefit from daily massage: so do full-term babies as well as older children. Massage therapy has been found to help children with all sorts of medical problems, including asthma, diabetes, cancer, autism, skin problems and psychiatric disorders, and even children who have been victims of sexual or physical abuse. Given all this, it would seem that we need to revise the general policy against touching by teachers and childcare providers.
In many cultures mothers are almost constantly in contact with their babies, carrying them in slings during the day and sleeping with them during the night. In Western societies parents generally spend less time holding their children. There is some evidence that babies who are carried in slings for a couple of hours a day spend fewer hours crying.