“Why Babies Love to Be Bounced: The Precocious Sense of Balance and Motion”.

This chapter talks about the vestibular sense, i.e. the sense of balance and movement.

A few interesting facts I learned:

• Already at 10 weeks, a fetus reacts to movement.

• Vestibular stimulation (chair spinning) can help the development of babies’ motor skills and reflexes

Children love motion from the moment of birth: rocking, jiggling, bouncing etc, and later on being spun, swung or flipped upside down. This is because they have a highly developed vestibular system – the sense for balance and the body’s movement.

The vestibular system is essential for maintaining head and body posture and for accurately moving most parts of the body, especially the eyes. It is what allows us to go joggin without feeling the world bounce up and down: the vestibular system compensates for the vertical movement of the body by moving the eyes up and down, so the picture stays constant.

The vestibular system is part of the inner ear. It is located in a hollow opening in the skull (the vestibule). There are two kinds of vestibular organs. The three semicircular canals detect head turns: each one is oriented along a different plane so they can detect rotation in all directions. The otolith organs are of two kinds. One detects linear movements (side to side or up and down) and the other detects movement with respect to gravity, such as tilting the head or lying down.

These organs all work fundamentally similarly. They have thousands of hair cells, covered with microscopic hairs or cilia. In the semicircular canals the hairs sit in a fluid, while in the otolith organs they are surrounded by a gel that contains tiny crystals. Either way, when the body moves, the cilia bend and send off a signal to the vestibular nerve. In the brain stem this signal is routed to the eyes (so that they can compensate for the motion), to motor neurons (to control the body) and to the cerebellum (where it is integrated with vision and touch signals to get an even more coordinated sense of balance).

Most of this happens below the level of consciousness, but some vestibular fibers go from the brain stem to the cerebral cortex as well.

Development of the vestibular system

The vestibular sense is very old and it therefore emerges early on in the embryo’s development. By seven weeks of gestation the three semicircular canals have formed, and between seven and fourteen weeks all the hair cells are formed. These immediately start attracting neurons, which also start growing in the opposite direction, towards the brain stem. The vestibular nerve is the first one in the entire brain to start myelinating. By five months the vestibular apparatus has reached its full size and shape, vestibular nerves have started myelinating and the entire system is quite mature. But other parts of the vestibular system do not finish myelinating until puberty.

Because these organs develop so rapidly and so early on, they are very vulnerable during gestation. An entire class of antibiotics (including streptomycin) is known to damage hair cells in both the vestibular system and the hearing part of the inner ear: early exposure can cause deafness as well as permanent damage to the balance sense. Any prenatal influence that can cause deafness will also threaten the vestibular sense, because the organs are structurally very similar. Such threats include the already-mentioned antibiotics, maternal infections (rubella and cytomegalovirus), hereditary factors and hypothyroidism.

By the 12th week of pregnancy the fetus will reflexively move its eyes when the position of its head changes. In the 8th month, sudden changes in position will activate the baby’s Moro reflex – flinging outward with arms and legs. The vestibular system also allows the baby to turn head-down in preparation for birth. Babies with defects in their vestibular system are much more likely to be born breech.

The vestibular function is central for several of the reflexes that are tested when assessing newborns’ neurological health. One is the asummetrical neck response. When a baby’s head is turned to the right (activating the vestibular sense) he extends his right arm and leg, and flexes the left arm and leg. If the baby was standing, this reflex would help maintain balance.

Another reflex is the traction response: when a baby is pulled from lying to sitting, he tries to hold his head up (even though he won’t succeed). The vestibular system senses that the head is moving forward, and tries to lift it to a vertical position, even though the neck muscles are not strong enough. There is also the doll’s eye reflex: when you turn the baby’s head to one side, the eyes will remain facing you, because the vestibular system helps stabilize the gaze.

A third reflex is also related to vision – the nystagmus response. Spin the baby in circles (on a chair, for example). When she stops, her eyes will move back and forth – fast in one direction and slowly in the other – because they continue to compensate for the motion even after it has stopped. This eye movement is faster in babies than in older children or adults. The vestibular system as a whole is over-responsive in babies, reaching a peak between six to twelve months and then declining. This is one of the reasons why toddlers are so wobbly. The vestibular system also needs time to mature: its contribution to maintaining balance keeps improving at least until seven years of age, possibly until puberty.

Vestibular development and the rest of the brain

The vestibular sense is strongly linked to general mental development, and deficiencies in this sense are frequently found among children with emotional problems, attention deficit, language disorders and autism. Mental development is cumulative, and since the vestibular sense is one of the earliest ones to develop, it provides a large share of early sensory inputs. These probably play a large role in the development of other motor and sensory abilities, which in turn play a role in the development of higher cognitive functions.

Vestibular stimulation

The opposite also seems to be true: there is evidence that vestibular stimulation can improve the baby’s brain. In one study, babies of various ages (ranging from 3 to 13 months) were exposed to chair spinning while sitting on a researcher’s lap, four times a week for four weeks. The babies loved this, and they also showed more advanced motor skills and reflexes than control groups who didn’t get any chair spinning.

Vestibular stimulation is also good for very young babies. It helps calm them when they cry: rocking, carrying and jiggling is more effective than simply holding the baby. In fact rocking without physical contact (e.g. in a baby seat) was more effective than physical contact without rocking.

Premature babies also benefit from vestibular stimulation: they gain weight faster, are less irritable, breathe better, and sleep better.

“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.

Temperature

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.

“How Birth Affects the Brain”.

This chapter describes the effects on the baby of labour, birth, and the drugs used in childbirth. The drugs, while beneficial for the mother, are probably overused from the baby’s point of view.

In general women today are quite careful about what they put in their bodies during pregnancy, so it can seem a little odd that many lose all caution on the last day of gestation, just when the baby is making the difficult transition to surviving on his own and will no longer have the benefit of his mother’s circulation to clear drugs out of his system. [...] All analgesics and anesthetics used in childbirth are serious controlled substances, in another league entirely from the occasional Tylenol or antihistamine that many women worry about during pregnancy.

A few interesting facts I learned:

• The birth itself may be triggered by the brain of the baby. That’s how it works in some other species.
• Stress hormones, which speed up breathing and heart rate in adults, have the opposite effect in babies, which helps them conserve oxygen during birth. They also give some last-minute help to mature baby’s lungs.
• For some reason, they don’t use nitrous oxide for pain relief in the US – it isn’t even mentioned in this chapter!

Birth is possibly the most traumatic event we experience, and the brain is affected the most, because the head is large relative to the rest of the body, and comes first. Besides physical trauma, labour can also hinder the brain’s oxygen supply, which is the greatest danger to the baby at birth.

Hormones

It is possible that birth itself is triggered by the brain of the fetus. (That’s how it works in sheep, where it has been studied most thoroughly.) The brain of the lamb fetus releases hormones which kick off other hormones (cortisol) which travel to the placenta and prepare it for the birth. In fact cortisol levels rise already through the last 3 weeks of pregnancy and help prepare the fetus’s organs for life outside the womb. The hormones involved are different in primates but the mechanism is probably similar.

During birth, each contraction compresses the baby’s head and body, and temporarily reduces blood flow to the placenta and the umbilical cord. This increases the levels of hormones that are associated with stress reactions in adults (high heart rate etc). In an infant they have an opposite effect, slowing the heart and the breathing. This helps the baby conserve energy and oxygen. The hormone levels remain high for 30 minutes after birth and then decline. This stress (which the baby doesn’t get in a C-section, unless it is preceded by several hours of labour) is very good for baby’s breathing and contributes to lung maturation. The hormones also seem to stimulate the nervous system – newborns are more alert during the first 2 hours of life than for many days thereafter.

Birth trauma

The baby’s head can be squeezed and molded somewhat without suffering damage. The fontanels allow the bones to slide without harming the brain. Sometimes the head does get damaged. The most common form of damage is bleeding between the skull and the scalp, which leads to swelling (bumps on the head). The bumps are no threat to the brain and almost always disappear within 3 months.

While the brain is well protected, the nerves outside the skull and the spinal cord are more exposed. Sometimes the nerves leading to the shoulder and arms (which exit the spinal cord near the neck) or to the face can be damaged if the shoulder gets stuck or the jaw is squeezed hard against mother’s tailbone. Neurons outside the spinal cord are capable of regrowing a path to their target, so this normally heals within months. Sometimes head trauma can tear the outer membrane of the brain, which can lead to permanent brain damage. Likewise if the spinal cord is damaged, the effects (cerebral palsy or paralysis) are irreversible. The risk of spinal cord injury is greatest in breech babies, if the head gets caught.

The greatest danger is that the baby does not get enough oxygen, which can happen if the umbilical cord gets compressed or the placenta is damaged. Experiments with monkey fetuses have shown that total lack of blood flow can be tolerated for up to 8 minutes. 10 to 20 minutes leads to brain damage, and any more leads to death. Partial oxygen deprivation can be tolerated for between 1 to 3 hours without evidence of harm. While 2% of babies suffer some shortage of oxygen, only 1 in 1000 suffers significant brain damage.

The greatest concern is cerebral palsy (CP), which is a general term for disorders of movement or posture caused by brain damage. It does not get worse as the child grows up, but it may look as it does, because it isn’t always evident until later – newborns are capable of few voluntary movements. Because of how blood vessels develop in the brain, the first area to be damaged by blood pressure in the brain is the motor cortex (in particular areas controlling the legs and spine) followed by areas for vision and hearing. Only 10-20% of CP cases are caused by birth damage. The rest are caused before birth – sometimes because of mother’s health problems such as high blood pressure, but more often they are completely unpredictable.

Fetal monitoring

Most interventions and technical innovations in modern obstetrics are aimed at preventing brain damage from hypoxia. Unfortunately there is little evidence that the measures have reduced the number of children born with CP or other disorders.

A very common procedure is monitoring the fetus’s heartbeat, either through the mother’s belly or directly through the baby’s scalp. In principle this provides useful information. But because the heart rate is only an indirect measure for the facts that really matter (blood pressure, oxygen to carbon dioxide ratio) it cannot be known for sure that a certain heart rate pattern means that the baby is in distress. Also, interpreting the patterns is very subjective and practitioners often disagree.

Studies have shown that fetal monitoring has not improved the baby’s chances of being born healthy. Monitored babies are just as likely to die, to need intensive care or to develop CP. And in one study the false-positive rate for predicting CP based on heart rate monitoring was 99.8%. This would be OK if diagnoses of fetal distress didn’t lead to C-sections, which can lead to serious complications.

Breech babies

The fetus can move around in the womb through most of pregnancy. Space gets tight in the last few weeks and babies then generally work themselves into the best position for birth: head down. Some don’t, and end up breech. Breech presentation is associated with increased risk for physical trauma (the head can get caught) and of asphyxia (the head comes out after the cord, so the baby cannot start breathing if there is trouble with the cord).

Because of this, most breech babies are delivered through C-section. This has led to fewer cases of brain damage. But C-section is really only necessary for maybe a third of breech babies – not if the baby’s position is otherwise straightforward and it is of average size. Nevertheless many doctors don’t like to deliver breech babies vaginally. Luckily there is an alternative – turning the baby from breech to head-down, before birth. This procedure (external cephalic version) succeeds in 50-75% of cases.

Forceps

Forceps use is associated with higher incidence of birth trauma and serious complications. However this may be due not to forceps use itself, but to the condition which made it necessary. Compared to C-section, forceps use does not appear to be more dangerous. However doctors have become more cautious and tend to opt for C-sections.

Obstetrical drugs

The vast majority of American women receive some sort of medication during childbirth to relieve pain. Opinions differ about how much the drugs affect the baby’s brain. Pediatricians tend to be most concerned; anesthesiologists least; obstetricians fall somewhere in between. In some cases anesthesia is necessary (C-sections) or makes childbirth easier. In some cases pain can frighten the woman, slowing down labour. Anesthesia may also protect the brain in difficult deliveries, by slowing down the baby’s brain metabolism. But at the same time, all pain-relieving drugs used in childbirth are serious drugs. While women are careful about what they put in their bodies during pregnancy, they seem to be much less careful during birth.

Systemic analgesics or pain relief drugs that reach the entire body are the most used painkillers in childbirth in the US. These are mostly opiates. These cross the placenta easily and reach almost the same concentration in the fetus’s blood as in the mother’s. In the mother’s body it takes an hour for the drug to reach peak concentration, and about 4 hours before the concentration goes down significantly. If the baby is born before the peak is reached, it doesn’t get much of the drug. If it is born after the 4 hours, the mother’s circulation helps clear it from the baby’s body. If it is born between 1 and 4 hours after the drug is injected, it gets the full concentration, and the baby body has to break down much of the drug. While this takes 4 hours in an adult body, it can take up to 20 in a baby’s immature body. And the breakdown byproducts can take days to clear. The most serious effect on the baby is breathing problems, which can be countered by another drug. Babies exposed to opiates during birth also tend to be sleepier and less active, and may have difficulty with breast-feeding because the suckling reflex is suppressed. It is unclear whether there are longer-lasting effects.

(Note by HT: in both Sweden and England nitrous oxide is the most used systemic analgesic, precisely because the dangers of opiates. It is not broken down by the body but dissipates quickly from the blood through the lungs. It also does not suppress baby’s breathing. However it doesn’t work for all women.)

Epidural anesthesia blocks pain signals from the lower half of the body only. A catheter is inserted between two vertebrae in the spine, so that its end is just outside the membrane surrounding the spinal cord. Pain-killing drugs are administered through the catheter. The mother feels virtually no pain, but loses little of the mobility in legs and pelvis, which explains why epidurals are so widely used.

The drugs can partly escape the epidural space and into the bloodstream of mother and fetus, but the amounts will be smaller than when the drugs are used systemically. Studies disagree about the effect of these drugs on the baby, but they are probably insignificant for most babies.

Epidurals also affect the baby more indirectly. The most common side effect for the mother is lowered blood pressure. If it drops too low, the fetus will get too little oxygen. This is prevented by giving the mother fluids through an IV, and if that is not enough, another drug is used to counteract this.

Studies have also shown that women who get an epidural have longer labours than those who get systemic analgesia. They are more likely to be diagnosed with “failure of labour to progress”, and more likely to have C-sections. However there is vehement disagreement about cause and effect here. An epidural slows labour, because it relaxes the pelvic muscles, reduces the mother’s urge to push, and may repress the baby’s own movements that help position him for birth. But it is also possible that women who get epidurals do so because their labour is already more difficult (because the baby is larger or less favourably positioned).

General anesthesia is rarely used for birth nowadays – only if a C-section is needed, and there is not enough time for an epidural. Even though the baby is usually delivered within 3 minutes, the drugs have time to cross the placenta and affect the baby. The baby tends to be less active and less alert, their reflexes may be disturbed, and they may have trouble breast-feeding for several days. In fact it is a paradox that a baby born to a sleeping mother can be awake at all.

“Prenatal Influences on the Developing Brain”.

This chapter goes through all the things that can affect the development of the fetus – mostly negatively. Nutrition (lack of), alcohol, drugs, chemicals, infections, stress, etc etc. On a more positive note there is a section about folic acid and how it helps prevent neural tube defects.

A few interesting facts I learned:

• There is enough folic acid in normal multivitamins for the needs of pregnant women. There is no evidence that the extra amount in specialist pills is useful (or unsafe, for that matter).
• A woman needs about 300 kcal extra per day during pregnancy, and 500–600 during breastfeeding.

Teratogens and birth defects

Life in the womb is characterised by lack of stimulation: dark, warm, confining, quiet. This seems to be important for early brain development: premature babies have a high risk of mental and neurological problems. Preterm babies who stay in a “womblike” environment stay healthier and develop faster.

The fatigue and nausea that many women experience may be another way to protect the embryo / fetus. The mother feels most miserable during the baby’s most vulnerable phase, and this keeps her from risky physical activities, and from spoiled and exotic foods.

But the womb is not immune from the outside world. Almost every drug, chemical, hormone, or infectious agent will cross from mother’s blood into the placenta to some extent. Substances that can cause fetal malformations are called teratogens. These are difficult to identify, because it’s a question of probabilities. The baseline probability of some kind of defect is 2–3%. Thalidomide, one of the worst teratogens known, caused malformations in 20% of exposed fetuses.

Most birth defects (65%) occur without any identifiable cause. Another 20–25% are linked to defects in chromosomes or genes – some inherited, some spontaneous. Known environmental or disease agents are responsible for 10%.

Teratogens are likely to have the worst effect during the first 3–4 months of pregnancy, when the organ systems are forming, but the nervous system is more sensitive because its development goes on throughout the entire pregnancy. The effects of teratogens on the brain are hard to identify, because brain damage can be caused by smaller amounts of teratogens than other congenital abnormalities. Also the effects on the brain tend to be more subtle and may even not be evident until in later childhood.

Very few drugs and chemicals have been tested for these effects so the general approach is “better safe than sorry” and pregnant women are advised to avoid heavy exposure to anything suspect. It also makes sense because many teratogens have a cumulative effect: the risk of one exposure is low, but exposure to one thing increases the damage done by others. For example, smoking increases the probability of other teratogens causing damage.

The flip side of this approach is that it sometimes leads to excessive worry and the stress of avoiding endless minimal risks may be more damaging than the risks themselves. A significant minority of parents even choose to terminate pregnancies because of their fears about such risks. A large number of such abortions took place in the US after the Chernobyl accident, even though the amount of radiation reaching the US was too small to measurably increase any risk.

Neural tube defects

One of the most important phases of brain development is the closure of the neural tube (from day 22 to day 28). If this fails in the spinal cord, it leads to spina bifida (part of the spinal cord developing outside the vertebrae). If this fails at the top end, the result is anencephaly (most of the brain fails to develop). The symptoms of spina bifida range from none to severe (paralysis); anencephaly is lethal.

Neural tube defects (NTDs) occur in 0.1% of pregnancies in the US. The rate of NTDs may be much higher because many miscarried fetuses have NTD, but this normally goes undetected.

NTDs are caused by several factors combined: genetic, ethnic, nutritional, chemical, etc. There have even been reports of seasonal variation. NTDs are more common when the pregnant mother has diabetes or epilepsy. Some drugs are known or suspected to be a risk; so is high body temperature (whether due to fever or a sauna).

Most NTDs can be detected early in the 2nd trimester by blood test, amniocentesis or ultrasound. When the neural tube fails to close, a certain protein present in the fluid in the ventricles leaks into the amniotic fluid and to the mother’s blood. The blood test is performed between 16–18 weeks of pregnancy, and if positive, it is followed up with other methods. All the methods together are able to detect ca 93% of NTDs during the 1st half of pregnancy.

Folic acid

The risk of NTDs is lowered significantly by folic acid (vitamin B9). The original study found 60% reduced risk for first-time NTDs, and 76% for women who had already had a pregnancy with NTD.

The official recommendation is that all women capable of becoming pregnant should consume 0.4 mg of folic acid every day. This amount is present in most standard multivitamin pills. Special prenatal pills contain a higher dose, which has not been proven more effective but appears to be safe. Folic acid is also present in many foods (leafy green vegetables, peas, beans, citrus fruits, liver, whole wheat bread) but these forms of folate are less easy to process by the body, and less stable when cooked, so some experts say it is hard to get the recommended 0.4 mg even with an excellent diet.

A problem with this recommendation is that many pregnancies are not planned. Because neural tube closure begins very early in the pregnancy (only 8 days after a missed period) many women will not be taking folic acid when it is actually needed. Many countries therefore require folic acid to be added to food. In the US it is added to all grains (flour, bread, pasta, rice, cereal). This extra amount is beneficial but small enough that women are still advised to take folic acid supplements before and during early pregnancy.

Nutrition

Unlike chemicals and drugs, general nutrition (getting enough calories) is less important during early pregnancy, and more important later, because the fetus requires less energy when it is small in size. From halfway through the pregnancy to about 2 years after birth, nutrition is very important for the growth and development of the brain. The earlier malnutrition begins, and the longer it lasts, the worse the effects. By comparison, starvation does not damage the brain in adults.

Babies of malnourished mothers are likely to be small. Within the normal range, birth weight and head size are not strongly related to later intelligence, but very small babies (birth weight less than 2 kg) have a higher risk of mental deficits. Optimally a pregnant woman should gain about 20% of her ideal pre-pregnancy weight, and bigger is generally better (up to a limit). A woman needs about 300 kcal extra per day during pregnancy, and 500–600 during breastfeeding.

When a pregnant mother is malnourished the placenta will not develop properly, which makes it even harder for the fetus to get the necessary nutrients. This sometimes happens in well-nourished mothers as well and is called intrauterine growth retardation. The problems are similar when there is more than one fetus competing for nourishment.

After birth, malnourishment leads to smaller brains, weaker dendrite growth and less myelin. Because neurons are produced early in the pregnancy, their number is not affected, but the number of glial cells (which produce myelin) is, because these are produced later.

Malnourishment often occurs together with other problems (the baby may be neglected, sick, abused, or just so hungry that it has no energy to learn), so it is hard to isolate the effects of malnutrition. However babies who are undernourished because of illness, but who are in a stimulating environment, do not suffer from mental deficits – a supportive environment can compensate for malnutrition. Also, children who are rescued early from malnutrition can recover most of their intellectual ability.

Chemicals and drugs

Nowadays drugs are assumed to be harmful in pregnancy, unless proven otherwise. For most of the known harmful medications, there are safer alternatives. Although over-the-counter medicines are generally less risky, it is best to avoid even those, unless absolutely needed. In particular, aspirin and ibuprofen are associated with pregnancy complications, and Tylenol is recommended instead.

Alcohol. Alcohol crosses the placenta easily, and will reach almost the same concentration in the fetus’s blood as in the mother’s. Prenatal exposure to high doses of alcohol causes fetal alcohol syndrome (face and head defects, growth and mental retardation, anomalies of internal organs), increases the risk of miscarriage, premature birth, and birth complications. In the brain, alcohol kills neurons and disrupts the migration of neurons and glia. Modest consumption (less than 2 drinks per day) appears to be harmless. As with most teratogens, there is probably a level below which alcohol has no effect on fetal development, but that level is not known.

Cigarettes. Smoking (including passive smoking) is one of the leading causes of low birth weight, and also increases the risk of miscarriage and premature birth. Nicotine interferes with the fetus’s breathing movements – this may also explain the higher risk of SIDS in babies born to smoking mothers. Nicotine also interferes with the neurotransmitter acetylcholine, affecting neuron structure.

Drugs. All of the widely abused drugs increase the probability of miscarriage and premature delivery, and to various sorts of behavioural problems.

Caffeine. Caffeine crosses the placenta and may even concentrate in the fetus. Caffeine has been found to be teratogenic in rodents, but does not appear to be a teratogen in humans.

Aspartame. In the body, aspartame breaks down into aspartate and phenylalanine (both normally present in the body) and methanol. The amount of methanol is minute. None of these appear to pose a risk.

MSG. High doses of glutamate overexcite neurons, which can damage or kill them. However glutamate does not cross the placenta well, and the amounts consumed are too small to be risky.

Both aspartate and glutamate pose a higher risk to infants and should be avoided in baby food.

Other chemicals. Based on current knowledge, pregnant women should avoid: organic solvents, oil-based paints, herbicides, pesticides, PCBs, vinyl chloride, carbon monoxide, hydrocarbons, mercury compounds, and other heavy metals (including cadmium, nickel and lead). The greatest risk occurs if any of these is inhaled or ingested.

Ionizing radiation

This includes X-rays and gamma rays. In adults radiation can lead to cancer; in a fetus it can lead to fetal death or birth defects, particularly in the brain. Exposure during the first 2 weeks after conception are generally lethal to the embryo. Between 2 and 8 weeks will likely damage other organs than the brain. Between 8 and 15 weeks (when neuron production is most intensive) brain damage is likely. After 15 weeks radiation continues to be dangerous but the risk of mental deficit is significantly lower.

Irradiation for treatment purposes (mainly cancer) is never advised during pregnancy – if it is necessary, abortion may be advised. Diagnostic irradiation should be used if necessary, but elective radiation (such as dental X-rays) should be postponed until after pregnancy.

Non-ionizing radiation

This catch-all term describes energy waves that may penetrate tissue but do not break apart biological molecules – light, microwaves, radio waves, ultrasound. The main factor limiting their safety is whether they raise the temperature of the fetus. They are generally considered safe as long as they don’t raise the temperature above 39°C. UV light does not penetrate deeply enough to harm a fetus.

Despite scare stories, exposure to microwave ovens, televisions, computer monitors, or low-frequency magnetic fields (from power lines) does not appear to be harmful. Evidence about MRI is mixed (women are recommended to avoid it during the first trimester), and for ultrasound the benefits far outweigh the possible minimal risk.

Infections

Several viruses are known to cause malformation of the brain or later mental deficits. As with all the other risk factors, the effects are greatest in early pregnancy.

Rubella (German measles): the woman may show no symptoms, while the fetus can be severely malformed. Luckily most women are immune by the time they are pregnant (due to earlier infection or immunization). A test is usually done at the first prenatal checkup.

Cytomegalovirus is a member of the herpes family. Again, adults often show no symptoms. This is the most common and most dangerous infection that a fetus can be exposed to. Luckily most of the population has already been infected before adulthood, and such recurring infections are less dangerous for the fetus. Most adults catch it from toddlers, so mothers in subsequent pregnancies are particularly susceptible. About 1 or 2 babies in 1000 is born with major brain or sensory damage due to CMV. No vaccine is available yet. Infection is spread via all bodily fluids, so pregnant women in contact with toddlers (own or others’) should be careful with hygiene.

Toxoplasmosis is a parasite often caught from animal feces (cats and mice), as well as raw meat, eggs and milk. Mothers’ symptoms are, again, often very mild. The chances of infecting the fetus are lower during the first 2 trimesters when it would do more damage. Still, 1 or 2 out of every 10,000 infants will be severely affected by toxoplasmosis – mental retardation, epilepsy, blindness, hearing loss. Avoid eating raw meat and eggs; wash hands and surfaces that have been in contact with these. Avoid all contact with cat litter.

Genital herpes can, in rare cases, be passed on to the fetus. Infection is more common during birth and can lead to severe brain damage. Antiviral drugs greatly lessen the severity of the infection.

Syphilis can cause severe damage to the fetus. Women are now routinely screened in early pregnancy, and penicillin is effective at blocking transmission.

Influenza is nowhere near as dangerous as the other diseases mentioned, but it is speculated that it may interfere with neuronal migration.

Hormones and stress

Most maternal hormones can influence the fetus in some way. Some cross the placenta and affect it directly. Thyroid hormone, for example, is crucial for neuron production, synapse formation and myelination. The fetus will start producing its own thyroid hormone halfway through gestation, but relies on the mother’s thyroid before that. Other hormones affect blood flow to the placenta.

Very high amounts of stress hormones are suspected to contribute to all sorts of problems: cleft lip and Down syndrome; newborn problems such as eczema, stomach ulcers and ear infections; even higher rates of miscarriage. These hormones can also interfere with almost every step of brain development. High levels of stress hormones in mothers may lead to higher levels of the same hormones in the baby, so babies born to stressed mothers are often fussier and more irritable.

Physical exercise leads to higher levels of some stress hormones, but lowers the levels of others. The current view is that exercise is safe for pregnant women, especially those who were physically active before pregnancy. (Avoid exercising in hot weather or at high altitude, and avoid scuba diving.)

“The Basic Biology of Brain Development”.

This chapter covers prenatal development of the brain and the nervous system, and an overview of the structure of nerve cells.

A few interesting facts I learned:

• The nervous system starts out flat as a pancake, then curls up into a groove, and then a tube.
• The brain cortex is made up of units perpendicular to its surface. More intelligent species have more grooves in their brains, and thus a larger surface.
• Initially too many connections are created between neurons, leading to noisy connections. This excess is pruned during early childhood.

Pre-natal brain development

Cell differentiation in the embryo starts with the development two tissue types: the endoderm (which later becomes the internal organs) and the ectoderm (which becomes the skin and the nervous system). Then a middle layer, the mesoderm (which becomes the bones and muscles) forms between them, along a track down the centre of the embryo. As this thread of mesoderm threads its way between the other two layers, the ectodermal cells it touches start turning into the nervous system. The embryo is now 19 days old.

The embryo is flat at this point, and so is the nervous system, so it’s called the neural plate. Over the next week this plate folds up into a groove, and then becomes a tube (called the neural tube). The top end is enlarged and will become the brain; the rest becomes the spinal cord.

So skin cells and nerve cells start out the same. The ones that come in contact with the mesoderm are folded inside the embryo and become nerves; the ones that stay outside become the skin.

By day 28, when the embryo is 3 mm long, the top of the tube separates into three lumps – the forebrain, midbrain and hindbrain. These then split further, so by 6 weeks all the major parts of the brain exist. The fluid-filled spaces between them are called ventricles.

The simpler, more basic structures form first. The spinal cord starts to function already at the beginning of week 9, causing the first fetal movements. The brain, on the other hand, doesn’t even have its final shape yet. After 3 months the mid- and hindbrain are mostly done, but the forebrain is not. Over the next few weeks the hemispheres grow, covering deeper parts of the brain, and connect to each other.

By 24 weeks the fetus is capable of surviving outside the womb: the lungs can breathe air, and the brain stem can direct breathing movements. But the cortex, the outer layer of the brain, is still far from done: it is smooth, without the characteristic “brainy” look.

The cortex is made up of lots of small processing units perpendicular to its surface. So the larger the surface, the more units the cortex can hold. More highly evolved species have larger brains, but also more and deeper grooves in their brains. These grooves grow during the end of pregnancy and the first year of life.

The brain continues to grow after birth. During the first year the brain triples in size, from 1/4 to nearly 3/4 of its final size.

Neurons and synapses

The brain is made up of two kinds of cells: neurons (nerve cells), and between them glia which provide structure and energy to the brain.

Each neuron is shaped like a tree: dendrites / roots that receive signals, a cell body, and an axon / trunk that splits into many branches and sends signals. A signal is transmitted electrically within a neuron, and chemically between neurons. The gap that the signal has to cross, from the axon of one neuron to the dendrite of the next neuron, is called the synapse.

Nerve cells are generated on the walls of the ventricles, the spaces within the neural tube. This process (neurogenesis) begins as soon as the neural tube forms (3 weeks), reaches a peak at 7 weeks, and is pretty much done by 18 weeks. 100 billion neurons are generated during the first half of pregnancy, which means half a million per minute! Only a few neurons are produced later, a very few even after birth. Glia on the other hand are produced throughout life.

All neurons start out at the surface of a ventricle. From there they migrate outward, along long glia. At the beginning the neurons only have a tiny axon, very few dendritic branches, and hardly any synaptic connections, so they cannot do much. They start growing new dendrites and forming synapses as soon as they are in place. This takes a lot longer than neurogenesis – it continues throughout pregnancy and most of the first year, in some regions even a part of the 2nd year.

How does a nerve cell find the right neurons to connect to? How does a path develop from a section of the eye to the right part of the visual processing centres in the brain? That’s not entirely clear yet. What is known is that neurons initially form too many synapses, with a lot of overlap and noisy signals. Synapses are then pruned – the ones that are used and useful get stronger, while the others regress. This pruning leads to more streamlined and coherent brain processes. The more stimulating the environment, the more synapses survive.

Myelin

Adult axons are coated with a fatty substance called myelin. This keeps nerve fibres from touching each other and interfering with each others’ signals. Before the myelin layer is in place, many nerve fibres are so leaky that they cannot transmit a signal all the way to the synapse. So even though the neurons are in place and connected, they don’t work properly.

Myelination starts at 5 months of gestation in the spinal chord, and in the 9th month in the brain. The process is slow, and like synapse formation it starts at different times in different parts of the brain – the more primitive parts first. It is not known if the child’s experience can affect myelination.

Myelin is 80% fat, and is produced by a special kind of glia. The number of these glia cells is sensitive to nutrition in early life, which is why malnutrition can affect myelination negatively. Myelin production is the main reason why children’s diet should have a high level of fat – children should drink full-fat milk during the first 2 years, for example. An extremely high-fat diet is even used to treat some forms of epilepsy in children.

The order of events, and critical periods

The nervous system matures from tail to head. The spinal cord and the brain stem are almost fully formed and myelinated by birth. The midbrain begins myelination just after birth. The inner parts of the forebrain follow later in the first year. The cerebral cortex is slowest. Sensory and motor areas mature relatvely soon, but the higher-order parts responsible for language, judgement, reasoning and emotion are still pruning synapses during in the teenage years.

The activity levels in the brain follow the same sequence: the primitive parts are most active first. Activity levels are estimated by measuring glucose use. Glucose use increases through childhood, reaches a peak between 4 and 7 years (depending on the part of the brain) and then decline. The peak is about twice the adult level. This overshoot-and-decline is similar to what happens with synapses. So it seems that the brain uses the most energy when the critical decisions are made about which synapses to keep.

Each part of the brain has a critical period, during synapse pruning, when it is permanently shaped by the child’s experience. Once a given brain region has passed the pruning stage, the opportunities for rewiring are very limited. Because of the order in which the brain regions mature, critical periods for basic abilities end earlier than those for more advanced skills.

Chapter 1, short and light, gives a brief overview of the nature/nurture issue, and explains the author’s reasons for writing this book.

Babies, as we’ll see, are not “blank slates” at birth. They come in to the world with all kinds of mental skills and predispositions, abilities uniquely suited to the critical needs of early life. Their brains are small, to be sure, but they are no miniature versions of an adult’s. The nervous system matures in a programmed sequence, from “tail” to head. By birth, the spinal cord and the brain stem – lower-brain structures that control all of our vital bodily functions – are almost fully developed and largely responsible for meeting a newborn’s essential needs: to survive, grow, and bond with caregivers.

This sequence continues after birth, as higher-brain areas progressively take control of a baby’s mental life.

But an obvious question is why babies are born with such primitive brains. Why, if development is largely preordained, do they not begin life with full vision and hearing, able to walk, talk, and do long division? According to one line of reasoning, it is our upright posture that is to blame: a bipedal lifestyle sets certain limits on pelvic size, so women can squeeze out babies only with relatively small heads – that is, babies whose brains are only partially developed. [...]

A better reason why we, and other intelligent species, are born with such poorly developed brains is so that we can learn. Babies’ brains are learning machines. They build themselves, or adapt, to the environment at hand.

After reading 2 chapters of this book I looked back and realised I couldn’t tell you a single thing I’d learned from it. So I’m going back to the beginning and starting over, this time taking notes. And since typing is faster than writing by hand, I’m going to post my notes here.