While babies are growing in the uterus, they are stretching and turning, and their senses are diligently processing incoming information. But are they able to form memories? And if so, do these memories affect the baby behaviour, representing an early form of learning? Dr Albrecht Peiper did not agree with the many scientists of his time who believed that the capability to form memories begins only after birth. He had observed that unborn babies reacted intensely when they first heard a car horn, for instance. But after they heard the horn several times, they reacted less and less and eventually stopped moving around. He proposed that the sound left a trace that inhibited further reactions to sound and wondered if this ability to remember stimulation was an early form of memory.
Later studies have confirmed and extended Peiper’s observations. The ‘memory trace’ that Peiper referred to is now called a habituation (getting used to things), which is considered one of the simplest, yet essential, learning processes. Habituation, which will play an important role all through life, is the ability to react less strongly to a repeated non-threatening stimulus. After their initial startle, the babies got used to the sound of the car horn. Ultrasound techniques have demonstrated that unborn babies as young as 23 weeks after fertilisation become accustomed to stimuli. Habituation appears first in girls, a further indication that the female nervous system is on an earlier schedule than the male.
Play that tune!
To find how long babies in the womb can keep a memory, Peter Hepper played a particular tune to mothers during the ninth month of pregnancy. He played it loudly and often enough that the unborn babies had a good chance to become familiar with it. One week after birth, the babies behaved differently when they heard the familiar tune from when they heard one that was new to them. But two weeks later, they didn’t distinguish between the familiar and unfamiliar tunes anymore. This shows that they could form a memory, but it was only of short duration at this stage of development.
We know that in the mature nervous system, a structure called the hippocampus is important for memory formation. It is therefore, of interest that this structure undergoes intense development at around 5 to 6 months after fertilisation. However, to store a memory for a longer time – over months or even years – the brain has to transfer it to the baby’s cerebral cortex. This transfer does not appear to be taking place at 2 weeks after birth.
The current knowledge about how memories are formed and learning takes place suggests that it is unlikely that unborn babies form lasting memories. However, basic processes involved in memory and learning are under way during the baby’s time in the uterus, forming the foundation for a head start at birth.
Too much, too soon?
Think focusing on unborn babies’ thoughts is modern psychobabble? Even before people had any idea of what babies are doing in the uterus, they considered trying to influence the child’s development. Writings from the 2nd to 6th century contain references to prenatal stimulation programmes.
The growing knowledge of prenatal development has sometimes led to the assumption that early stimulation might speed up brain development. However, no scientifically established evidence shows that stimulation of the unborn child, for example, by music, leads to an accelerated brain development. Any benefits are likely to be due to the increased interest of the mother in her pregnancy and the resulting positive effects on her lifestyle both before and after the birth of her child. The natural environment of the uterus provides all the stimulation the baby’s brain requires.
If additional stimulation could speed up development, premature babies, exposed earlier than normal to the outside world, would be ahead of babies who spent the full term in the womb. But our own studies show that, in spite of their earlier exposure to outside stimulation, babies born after only 32 weeks do not have a head start over full-term babies.
Better in than out
Dr Petra Huppi used behavioural scales and magnetic resonance imaging (MRI) techniques to monitor and compare the development of premature babies and those born at full term. She compared the preterm babies at their expected due date at 40 weeks to term babies born at full term. In spite of their 8 week head start, the premature babies’ development was delayed. The 8 weeks that the term babies had spent in the uterus were apparently beneficial. Although the development of brain structures is not speeded up by extra stimulation before birth, negative influences can impair a baby’s brain development. Alcohol, nicotine, drugs, malnutrition are known risk factors, as are X-rays and some infections.
If you are racing around from one appointment to another, struggling to balance school schedules, and deadlines, to say nothing of trying to find a quiet moment to collect your thoughts, you may worry about what effect your daily hassle could have on your baby’s brain. As early as 480 BC, Empedocles suggested that the development of the embryo could be guided and interfered with by the mental state of the mother. And 1,000 years ago in China, ‘prenatal clinics’ were established to keep mothers tranquil, which were thought necessary to maintain the psychological health of the unborn baby.
Mind the stress
In the early 1970s, scientists began to approach this question in a systematic way. Researchers in Canada studied the relationship between a mother’s stressful situations during pregnancy and the baby’s postnatal development. The investigators found that mothers who suffered constant high, personal tensions during pregnancy – mainly martial discord – had children who had an increased risk for eczema and tended to reach motor milestones later that infants of mothers whose pregnancies had been more relaxed. The babies also tended to be more fretful and restless and have difficulty quieting down. The authors suggested that changes in the hormone system of the mother resulting from stress could affect her unborn child. We now know that prolonged and severe stress during pregnancy can have serious consequences. Reduced blood flow to the placenta may restrict the baby’s growth and play a role in the condition known as ‘small-for-date’. But what about stressful events that are part of our normal everyday routines? You are frightened by a sonic boom, your 2-year-old races out into the street, your boss criticises the report you worked on all weekend. Your nervous system reacts to all these sudden events by causing a surge of adrenaline into your bloodstream. This surge may lead to a restriction of blood flow to the uterus, similar to the effects of a mother’s smoking. Your unborn baby detects the change and ‘sympathises’ with your upset condition: his nervous system also produces more adrenaline, causing a temporary change in heart rate and body movements. But after a few minutes, everybody settles down, and the nervous systems of both mother and baby go back to their usual settings.
If a mother’s anxious, her body produces more of the hormone cortisol, which mobilises the body in times of stress. Some of the cortisol passes directly to the foetus and some acts over the placenta to stimulate the baby’s own endocrine system. High levels of mothers’ reported anxiety, particularly during the latter part of pregnancy, have been linked to a cluster of behavioural problems that appear in early childhood. These include hyperactivity / inattention, particularly in boys, and emotional problems in both boys and girls.
In a recent study, J K Buitelaar and colleagues asked pregnant women to make notes about their daily hassles and pregnancy-specific anxiety, and periodically collected samples of cortisol present in their saliva. These data were then compared to temperament questionnaires and tests of infant development at 3 and 8 months. The investigators found a link between high levels of anxiety in the mother and infants’ lower scores in mental and motor development.
The same group also studied the relationship between mothers’ late pregnancy cortisol levels and videotapes of the infants’ behaviour in the home at intervals between 1 and 20 weeks of age. The infants of mothers with high cortisol levels tended to show more crying, fussing and negative facial expressions and were described by mothers as more ‘difficult’. The differences between the infants of the high and low cortisol group were the greatest at the youngest ages – that is, between 1 and 7 weeks.
So, a baby’s brain is constantly shaped by his experiences. This gives parents the opportunity to counteract the effects of the prenatal stress by adjusting their childcare techniques to meet the needs of the child. This means that babies born following a particularly stressful pregnancy may need an especially calm, consistent environment.
We’re all individuals
Babies often react individually to prenatal ultrasound examinations. Some become aroused and make strong movements, while others react less noticeably. Peiper had already made similar observations with his car horn, although he didn’t pursue the question further. The differences could be due to the unborn baby’s momentary alertness, or might be something to do with temperament.
A 1999 study confirmed what mothers have experienced all along: that babies show individual patterns of activity while still in the uterus. At the middle of the 8thmonth, investigators measured the rate of the unborn baby’s general spontaneous movements on 3 different occasions using ultrasound techniques. Each child showed a clearly individual pattern of body movements. The researchers the compared these data to the baby’s activity during the 2ndand 4thweek after birth. The babies who moved more often or kicked around with greater energy before birth were the ones who were also more active during their first months outside the uterus. These observations showed that children are born with certain individual traits, influenced by genetic factors and by conditions in the uterus.
Given that a baby’s birth weight is only 5% of what he will weigh as an adult (and the weight of his brain is already 30% of the weight of an adult’s), it stands to reason that your baby might be doing a wee bit more inside that bump of yours than simply staring into space. Now, isn’t that amazing?
To find out more, read the complete book, A Good Start in Life: Understanding Your Child’s Brain and Behaviour From Birth to Age Six.