This website is intended for healthcare professionals only.
Fri, April 1, 2016
Author: HUGO LAGERCRANTZ, Paediatrician and Senior Professor. Karolinska Institutet, Editor-in-chief Acta Paediatrica
Until the 1970s, it was thought that the newborn brain was a clean slate. The newborn baby saw the world around it as if in a fog and perceived sound, such as when the mother spoke to the baby, as a buzzing jumble of noise. The infant should be left in peace and only be picked up to be breastfed or for a nappy change. Nowadays, we know that the infant recognises faces and human voices. They express feelings such as pleasure and distress. New imaging methods have shown the occurrence of very high activity levels in the cerebral cortex. The newborn brain is by no means a clean slate as was previously thought. This article discusses how the infant perceives itself and the surrounding world using its senses, how it learns its native language and how it develops its “soul” or consciousness.
The newborn baby’s senses
The sense of sight is not yet fully developed in the newborn baby, as it is a little short sighted. When it looks at its parents they are a little out of focus. However, they seem to be able to understand if their mother or father is happy or angry. If the parent opens their mouth wide or pokes out their tongue, the newborn baby replies by mimicking. It seems that they can recognise the human face right from the start. A baby is able to mimic because humans are equipped with so-called mirror neurons, which enable mimicking, and this is a pre-requisite for learning.
“ The sense of smell develops early in the infant. The infant quickly learns to recognise its mother’s scent. ”
Hearing is more developed than sight in the newborn baby. If a red ball is held up on one side of the infant and a bell is rung on the other side, the infant turns first towards the source of sound. Even as a foetus, the infant starts to listen to the mother’s speech and learn her language. The newborn baby still has some liquid in the auditory canal, which means that, just like in the foetal phase, the infant hears everything from an underwater perspective.
The infant’s sense of smell develops early. It quickly learns to recognise its mother’s scent. The infant is more interested in the smell of a swab soaked in its own mother’s breast milk than in one soaked in another mother’s breast milk. In one study, one of the breasts of newly delivered mothers was washed and their babies were placed below this breast. The infants always sought out the unwashed breast, probably guided by the scent. It is possible to measure how the infant reacts to smells using so-called near-infrared spectroscopy (NIRS). The head is screened with a reddish light, which is reflected by the red blood cells. Depending on the blood flow to the brain’s olfactory centre, which is behind the eyeballs, it is possible to get an idea of how the brain perceives smells. The newborn baby is seen to react even to the first milk (colostrum). They also seemed to like vanilla, but reacted negatively to disinfectant.
The sense of taste is also well developed in the newborn. If you let an infant taste something bitter, sour or salt it grimaces. The infant definitely prefers sweet things, such as milk. The sense of smell is important so as to be able to avoid things that are harmful. Interestingly though, it seems that the baby can learn to like certain tastes, such as garlic, if the mother has eaten a lot of this during pregnancy.
The sense of touch develops very early in foetal life. Even when the foetus is 2-3 months old it reacts if it is touched. After 5 months of pregnancy, the foetus reacts to pain if, for example, a blood sample is taken. The question is, if the foetus is aware of the pain. As soon as the baby is born, however, it is aware of pain. Not so long ago it was thought that babies were not aware of pain, in which case surgery could be performed without anaesthetic, although this was considered dangerous.
We now know that pain signals reach the cerebral cortex and the infant is probably aware of pain. It is even possible that infants are more aware of painful procedures than adults, as the bodies own pain-relieving mechanisms are not yet fully mature.
When the infant is about 2 months old it goes through a revolutionary phase in its development. The infant has developed a response smile from 6 weeks of age. The infant starts to more actively communicate with its parents. If the mother maintains a frozen facial expression, the infant becomes desperate and is not happy again until the mother talks or smiles.
The baby’s forebrain starts to become more active. A substantial synapse development takes place in both the visual and auditory cortex. The baby can see better and more in focus. It follows movements in the room with its eyes. The cerebral cortex starts to be able to take over control of certain brain functions, such as breathing, which is important for the baby to be able to babble and talk. The baby’s movements become more purposefully controlled and primitive reflexes start to disappear. If the infant’s attention is distracted, it is possible to make its spontaneous crying stop, which can also be due to the cerebral cortex taking over control of lower brain functions.
The baby already has the ability to understand that objects are still there even though they cannot be seen, which was previously not thought to develop before 9 months of age. The infant can, for example, remember a dummy that is taken out of sight.
Four to six months
At four months of age, very substantial synapse development takes place in the visual centre of the brain. The sight pathways are refined by the influence of visual impression, that is to say that the active sight pathways are reinforced and those that are not used disappear. This is also an important process in the development of the perception of depth, which is now starting. Likewise, the infant starts to get a richer colour vision and see the scenery and the sky. The baby understands not only the adult’s way of speaking to them but also their facial expressions and lip movements. It is easier to comfort a crying baby by distracting them with lulling, songs and nursery rhymes.
Six months to one year
becomes more playful and adventurous. Babies like song and music, and gladly clap their hands with joy. They also start to be suspicious of strangers. From the age of 7 months babies develop a working memory, that is to say they can keep a thought in their head, which can be tested with different kinds of hide the object games. During the second half of the infant’s first year it is primarily language (see below) and therefore also the social brain, which develop.
If they are neglected, frightened or even abused, this can have particularly severe consequences at this age. This could be detected in brain X-ray images from the Rumanian children from orphanages where they had been kept totally isolated and neglected.
The baby is a language magnet
Language starts to be learned even in foetal life. Swedish babies have been shown to recognise the typical Swedish vowel “u” better than American babies, who are better at recognising the English e-sound, that is “iii” in Swedish. This has been tested by recording dummy- sucking in newborns who listen to different vowel sounds. The baby is like a language magnet and learns all kinds of phonemes (syllables) that they hear. In principle, the infant can learn all languages. However, then the window for language learning is partly closed, that is to say the neural circuits that are not stimulated disappear. The most famous example of this is that Japanese people cannot distinguish between l- and r-sounds, as these sounds do not occur in Japanese. This means that a Japanese person cannot distinguish between the phrases “fried rice” and “flied lice”.
Figure 1. Number of new synapses in the brain’s language centre
In a famous study, 9-month old American babies were taught Chinese. Students from China played with and read aloud to American babies in Seattle for a couple of hours a day during a period of a couple of months. When the babies were then tested it was found that they understood the Chinese words just as well as the English words. Infants cannot say very much but their ability to understand words was tested by recording brain activity using EEG. When the study was repeated, but instead, the children were allowed to watch and listen to Chinese on DVD, this had no effect on language learning. Therefore, direct mental and physical contact with the infant is necessary, and the infant should be constantly encouraged.
The baby “absorbs” the native language that it is fed during the first years of life. It is no problem for the baby to learn one or two additional native languages, although preferably before the age of 3 years. The baby does not seem to mix the languages up as long as the parent speaks their own native language to the baby. But if, for example, a French father who is married to a Swedish mother starts speaking Swedish with his child it can be confusing. The importance of learning another language early is particularly important for immigrant children who should be able to start early at a Swedish speaking pre-school. After the age of five years and up to puberty it is still relatively easy to learn a second language, but it will not really be the same as the native language. Other parts of the brain are used instead.
The infant’s “soul”
The word, soul, is understood mainly as a religious concept, but in my view, it corresponds to the English word “mind” or consciousness. When do infants start to be conscious of themselves and when do they form their own opinions? The newborn baby appears to have a certain sense of self right from the start. The baby reacts more when stroked by the mother than if stroking itself. It seems to have a certain body image. The foetus sleeps nearly all the time, even if it sometimes may open its eyes and express feelings through facial grimacing. Directly after birth, the newborn baby wakes up and becomes aware of itself and the world around. As mentioned above, the baby looks more at a face than an abstract figure. It prefers human sounds to other sounds. It also seems happy if it is not too hungry or subjected to being prodded and such like. The birth is tough and painful even for the infant, during which high levels of stress hormones (noradrenaline and adrenaline) are released into the blood. These, however, have mostly a stimulating effect on the infant. According to earlier research, activity in the cerebral cortex was considered to be fairly low in newborns. However, examinations using a magnetic resonance imaging camera have now shown that there is a very high level of spontaneous activity in the cerebral cortex even in infants. Nearly half of all the blood glucose goes to the newborn brain, which can be compared to 20% in adults. The brain’s “stream of consciousness” can therefore be found in the newborn baby, even if it is different to the adult’s brain.
As mentioned above, the infant is more aware of what it experiences than was previously thought. It can be said that the infant is aware of a lot of sensory impressions that it takes in, maybe more than adults who are more focussed in their awareness. The ability to recognise oneself in the mirror comes later, however, at about 18 months of age, and the ability to understand how others think comes at 4 years of age (theory of mind). The infant lives more in the present and does not think so much about what has happened and what is to come. The synapses where the episodic memory is stored disappear and what happened before the age of three years is not remembered. However, strong memories of odour or pain remain in the brain for a long time. The languages that are learned early are remembered provided that they continue to be practised through listening and speaking. If this does not happen, the other languages that the small child has learned, for example during a stay abroad, disappear.