Nursery World - A Unique Child: The Developing Brain, part 1

In its last few weeks in the womb a baby is already busy learning, says Annette Karmiloff-Smith, in the first of a new series on the developing brain.

The womb is a unique environment that constantly adapts to the changing needs of the developing foetus. But nourishment and physical growth aren't the only purpose of life inside the womb. Interestingly, we used to think of the foetus as passively waiting to be born, floating in the amniotic fluid. Far from it; babies are busy learning, even before birth.

Exciting new research has shown that in the final trimester, the foetus is able to discriminate different auditory stimuli, store them in memory, and subsequently recognise them at birth. These include: a piece of music that the mother listens to repeatedly while pregnant; the timbre of her voice compared with that of other females; the sound patterns of her mother tongue; and even the taste of her favourite foodstuff. Indeed, by the time the foetus reaches six months' gestation, taste buds have developed in its mouth such that it will be sensitive to strong changes in the maternal diet that flavour the amniotic liquid.

Far more than the sense of taste, however, it is the sense of hearing that develops most during intra-uterine life, starting to come on line as early as 15-20 weeks' gestation. But it is particularly in their final three months that foetus' brains are busy processing a wide variety of sounds. So, rather than a calm waiting room, life inside the womb is very stimulating and plays an important role in the early development of the foetus' brain and different senses.

LEFT AND RIGHT

Some scientists argue that handedness is already apparent during intra-uterine life. Using ultrasound scans, one study observed foetuses at 15-21 weeks' gestational age and found that when sucking their thumb, 71 per cent of them sucked their right thumb, a percentage that rose to 93 per cent by 36 weeks. In other words, the difference between the percentage of foetuses sucking their right thumb versus their left thumb mirrors the high percentage of right-handers in the outside world, suggesting that the beginnings of brain lateralisation are already developing in the womb.

Interestingly, most babies find it very easy to locate their mouths before they are born, because in the womb they are solely guided by their sense of touch, uninhibited by gravity or the sight of their own hands.

In sucking its thumb, the foetus isn't expressing hunger or tension, but actually learning about touch. It mirrors what happens after birth, when babies initially put everything into their mouths. Early on, the tongue has far more nerve endings than the fingers, so in early post-natal life the baby uses its mouth to explore the size, texture and shape of objects.

The foetus can also be observed holding on to the umbilical cord, which is long and flexible and has a grooved surface - a different tactile sensation compared with the thumb. So, by sucking its thumb and holding on to the umbilical cord (see Figure 1), the foetus is already beginning in the womb to use the sense of touch to explore its environment.

Mood reactions

As the foetus develops and becomes increasingly attuned to intra-uterine life, it also begins to react to changes in its mother's mood. Emotions release a range of chemical responses into the mother's bloodstream, which are then carried around her body, penetrating the placenta, where the chemicals affect the foetus too. The unborn baby will thus experience a sense of calm when its mother's endorphin levels rise or a quickened heart rate when maternal epinephrine levels increase.

Psychologists are becoming increasingly interested in the long-term effects that these pre-natal emotional experiences might have on the baby's postnatal behaviour. For example, studies suggest that higher foetal heart rates and motor activity predict some aspects of newborn temperament, such as irritability.

Scientists used to think it was impossible to test experimentally the capabilities of children before they were able to speak, and that at best we could simply do observational research. But in recent decades, researchers have devised ingenious techniques to study the foetus and the pre-linguistic newborn experimentally.

Using ultrasound scans to record 'startle' reflexes or changes in the rate of leg movements, as well as monitors to record changes in heart rate, researchers can now measure foetal reactions to stimuli from outside the womb. For example, if a bright light is shone on the surface of the pregnant belly, the foetus will react by increasing its movements, indicating that the baby's visual system is beginning to develop even before it sees the outside world.

AUDITORY ABILITIES

More striking are the foetus' auditory abilities. If, during the final trimester, a loudspeaker playing a recurring sound is placed on the mother's abdomen, and then that sound is suddenly altered, the baby's heart rate or kicking rate will be modified too, indicating that the baby's brain has registered the change in sound. So, scientists can quantify the exact moment when leg kicking or heart rates change, and map that to the timing of the introduction of a new sound (see Figure 2).

The same applies to more complex auditory input, like pieces of music or human voices. Here, too, the foetus will detect and react to changes that the scientist can quantify. Once born, the baby will actually recognise the sounds it previously heard as a foetus in utero. So, if the newborn is tested with a tune heard repeatedly during the latter part of intra-uterine life, for example, the 'EastEnders' theme tune, it will prefer to listen to that tune over another tune the mother did not listen to.

We can assess this in newborns by using what is called the non-nutritive high-amplitude sucking techique (see Figure 3). The dummy that the baby sucks on is attached to a computer that produces stimuli as a function of the baby's sucking rate. If the baby sucks slowly, the computer will produce an unfamiliar tune, but if the baby sucks harder it will hear a familiar tune.

By measuring differences in babies' sucking rates, scientists have shown that newborns suck at a faster rate to hear a familiar tune heard previously in utero. The same applies to the mother's voice. Even though it sounds very different through the amniotic fluid compared with its sound in the world outside the womb, foetuses must have stored quite an abstract mental representation of the quality of their mother's voice in the womb, because at birth they can discriminate it from the voices of other females.

As a highly complex system vital to human communication and socialisation, language presents a special challenge to the developing brain. The foetus begins to process the sound patterns of speech before birth. For example, if, in the final trimester, an expectant bilingual mother speaks mainly English in her day-to-day life but an Italian friend drops in for a chat, the sounds from another language will instigate a reaction in her foetus as it becomes sensitised to the novel input.

Its heartbeat may quicken, or it may begin to kick more vigorously, as its brain registers the new experience. Obviously the foetus is not reacting to differences in words or grammar! Rather, it is the new intonation and stress patterns from another language family that it recognises as different from its mother's usual speech.

BRAIN IMAGING

Among the most amazing advances in foetal research is the fact that scientists can now measure foetal brain activity in real time. At Nottingham University, neuroscientists use a 0.5 T scanner, which is a low-field strength compared with that used in most brain-imaging studies. The greatest challenge to foetal brain scanning is motion, because one can hardly expect a body floating in liquid to keep still. But data analysis techniques are being developed to take into account the movement of both foetus and mother.

In addition, foetal brain imaging studies are now being performed late in pregnancy, when the head is already engaged, resulting in fewer movement problems. The scientists have been successful in detecting complex brain activation in about 50 per cent of foetuses scanned, demonstrating quite large increases in blood flow to different brain regions.

There is surely much more for scientists to discover about life in the womb. However, it is already clear that in the latter part of pregnancy, the foetus is busy learning and is significantly more sophisticated than we ever imagined.

Annette Karmiloff-Smith is a professorial research fellow, Department of Psychological Sciences, Birkbeck, University of London. For information on Birkbeck's Centre for Brain and Cognitive Development, visit: www.cbcd.bbk.ac.uk/babylab

REFERENCES

- Hepper, PG (2007) 'Prenatal development', in Introduction to Infant Development (2nd edition) Slater, A, & Lewis, M (eds), Oxford University Press, pp41-62

- Hepper, PG & Shahidullah, BS (1994) 'The development of fetal hearing', in Fetal and Maternal Medicine Review, 6:167-179

- Karmiloff-Smith, A (1995) 'Annotation: The extraordinary cognitive journey from foetus through infancy', in Journal of Child Psychology and Child Psychiatry, 36 (8), 1293-1313