To make sense of its world a brain has to learn - and keep learning. The brain spends decades upgrading itself from dial-up internet to high-speed broadband and even then the job is not fully completed. Explore your amazing mind with us and see how it develops from birth, through the teen years and into old age. And be amazed.
With 100 billion cells and an intricate network of neural fibres the human brain is the most complex system in the known universe. Its processing power and versatility far exceed that of any computer.
Its ability to organise, store, recall and use information provides the basis for learning. Only about half the mass of the brain is composed of grey cells. The rest is fatty white matter or connecting tissue that keeps nerve signals from sputtering out or cross-firing during transmission.
Each of the four lobes making up the two hemispheres of the brain has numerous folds, which mature at various times. This is because the chemicals that encourage brain development are released in waves and explains why there are"prime times" for specific kinds of learning and development. Various parts of the brain control various functions.
Thinking, planning and remembering happen mostly in the uppermost, ridged portion of the brain (cerebral cortex) for example.
Although the basic building blocks of the human brain are all present at birth, the brain is still in a surprisingly unfinished state. The specialised nerve cells (grey matter, or neurons) are not yet connected in networks. Neurons have to form connections through "output" and "input" fibres which send and receive impulses to and from other neurons.
As a child grows each cell grows bigger and heavier because the conductive nerve strands multiply. As the "input" fibres (dendrites, which look like hairs or fine wires) branch out, they form connections that can receive signals from as many as 15 000 other neurons.
This complex network is sometimes referred to as the brain's wiring or circuitry. Forming and reinforcing these connections are the key tasks of brain development. If specific wiring is not used repeatedly or often enough it is eliminated.
The baby brain
Six months into pregnancy the womb is a place of significant learning. Newborns recognise music and voices they heard as a fetus. Newborns have the best possible chance of coming into the world with a healthy brain.
The brain is so sensitive to its environment that even identical twins have visible differences in brain structure by the time they're born. These are caused by the minute differences in nutrients and sensory stimuli experienced by each fetus.
after conception the brain's main structures are visible. The primitive structures at the base of the human brain develop first.
The fetus responds to pricking but doesn't feel pain; this is just a reflex. The thinking brain is only an unconnected mass of cells.
The brain is sufficiently wired for the fetus to hear, smell, taste and blink when a bright light is shone on the mother's abdomen.
Fact: A fetus' brain produces twice as many neurons as it will eventually need. Not a bad safety margin! Most of the excess neurons are shed in the womb.
Birth and beyond
Your baby's brain contains as many nerve cells (neurons) as it will have as an adult but has relatively few connections (synapses) between them.
Sadly, most of these cells will not be replaced if they die. Exceptions include the cells involved in smell and taste in the olfactory nerve which are continually replaced throughout life.
On the day they're born, babies can recognise their mother's face, voice and smell. Your little Einstein! To do so a baby uses structures in the more primitive core of its brain that matured in the womb. After a few hours a baby can mimic facial expressions. Yes, it brings tears of happiness to your eyes, but this is just a reflex and takes on meaning only once the cortex develops.
Due to chaotic connections between neurons and jumbled pathways a newborn's experience of the world is very different from our own. Young babies display simple emotional reactions, and although they're not conscious of their emotions, these experiences may be stored in a primitive part of the brain called the amygdala, one of the first to function.
The brain is the fastest growing organ in the body. The forest of connections is soon pruned into a more efficient network. As the brain gradually discovers which connections deliver focused impressions, some cells die and some links between neurons are severed.
Meanwhile your little genius is experimenting by banging objects, for example, and learning to interpret sensations in a way that makes sense of his world. This explains why suddenly at six months, kids develop "stranger anxiety"; they now see the world at a more conscious level.
At about eight months babies know that when a toy is hidden under a blanket, the toy still lies beneath it. When adults play peek-a-boo babies recognise and understand simple spatial relationships.
This happens because the outer part of the brain becomes active. The frontal lobes also become active during the first year so baby starts to make simple decisions such as choosing between two toys.
Motor-skill development starts shortly after birth with the larger muscles (such as the neck, arms and legs) and progresses to increasingly smaller muscles (such as fingers and toes), in the second half of the first year.
It's vital that you stimulate your baby; it will influence the way in which she learns and interacts with others throughout life. The infant's brain forms and retains only those synapses that it uses frequently.
Connections that are used become permanent. Some doctors reckon it's possible that if loving interaction with caring adults is absent, the brain might make different connections. A lack of sensory experiences leads to loss of brain function.
Kids usually understand what is said to them before they can speak. This is because infants begin to understand spoken language when development in one section of the left side of the brain takes place.
They start speaking only some months later due to increasing maturity in an adjacent area. The integration that occurs in the second year of life makes all subsequent development much easier.
Fact: The temper tantrums of the terrible twos are a direct result of toddlers' verbal inability to explain what they want
What can go wrong?
During the first three years of life the brain is at its most vulnerable. Its development is an ongoing process and any trauma or disease such as meningitis spells disaster because it affects the development process of the brain.
Various genetic conditions such as Down syndrome or exposure to alcohol, drugs and infections acquired by the mother during pregnancy, such as German measles, impact severely on the development of the brain. After birth other infections such as meningitis or injury (either accidental or from abuse) can have a devastating effect.
An ultrasound scan can pick up structural brain abnormalities but disorders of brain function will not be detected.
Windows of opportunity
Various brain functions develop optimally at various ages:
Mathematics and logic
The child brain
Your child has a vocabulary of 50 to 200 words, plans more complex actions and performs them more effectively. Language functions are becoming localised in the right or left hemisphere of the brain. The size of the brain and its relative proportions are similar to those of an adult.
Why do you hear the word "no" so often? Your toddler is developing his sense of self due to the gradual refinement of the limbic system (the part of the brain that governs our understanding of self, our emotions and appetite). He is expressing his newfound independence . . . although a moment later he'll cling to you for reassurance and security.
If we cannot remember much of our first two or three years of life it's because the hippocampus, where the brain stores long-term memories, does not mature until then. Of course memories may also be linked to the increase in language skills.
Awareness of the body is developed through the sense of touch. Playing with toys aids your toddler's sensory development and teaches him to handle things such as zippers. Climbing is an important skill to learn, as it requires balance, visual perception and a sense of self.
Your kid becomes a mature being who can talk and relate to many people. His brain develops rapidly and builds up memories about procedures. Whole picture concepts begin to form, helping him to figure out how the world works. Images, movement, rhythm, emotions, intuition, speech and integrated thought are established.
Take him to the playground. Swings, slides, merry-go-rounds, monkey bars, seesaws and sandboxes are the perfect place to integrate the developing nervous system and sensory experiences.
As finer motor skills develop he learns to use various tools such as scissors and cutlery. For little Johnny to put on clothes or tie his shoelaces he needs all the sensory information that has been stored in his brain during earlier activities.
Early childhood learning shapes the growing brain, and as soon as your child is ready develop her fine motor skills through activities such as drawing and playing a violin or piano - musical fingering ability starts at about age five.
By the age of six there are more connections between cells than there are in adulthood and unused neural connections begin to die.
While most children can recognise themselves in a mirror by the time they're two years old, the world revolves around them until they are five or six when they begin to realise that other people may see and feel life from quite a different point of view.
They also learn that thoughts and imaginings are distinct from real events in the outside world.
Stressful experiences shape a child's developing brain. If they're faced with physical or emotional trauma, stress may cause brain cells to die and reduce connections between cells in certain parts of the brain, which is why children struggle to learn, think and act appropriately in stressful situations.
Meaningful experiences really do produce rich brains.
Kids are able to reason (and argue!) with you, and speak well enough to communicate ideas, needs and interests. A striking growth spurt can be seen from age six in areas connecting regions of the brain regions specialising in language. It's a critical period for learning languages; from the age of 12 this growth drops off sharply.
At the age of eight a child's sense of touch, gravity and balance is usually well established. He can balance on one leg and walk a narrow beam. The ability to plan and sequence a number of motor activities should be evident and these will be refined in the next few years.
He develops more sophisticated memory skills for increasingly complex activities. He discovers that information becomes easier to learn once it's organised and that memory is strengthened by repetition and practice. He also creates associations between new and existing knowledge.
All of this happens because his mind becomes more logical. Whole brain processing occurs because the bundle of fibres connecting the left and right hemispheres of the brain is further developed and reinforced by a myelin sheath around the connections (much like the insulation around an electrical wire). If his attention span is short, don't worry - this part of the brain does not develop fully until puberty or even later.
What can go wrong?
Plasticity (the ability of the brain to form itself anew) is key at this stage. If a child's brain loses a particular focal area through injury or stroke, another part of the brain can take over that function, provided it happens at an early enough age.
In children it is even possible to remove half the brain and the remainder will regain its function. This is in fact what happens in an extreme operation for epilepsy. If the whole brain is damaged, however, plasticity cannot occur.
Scientists are not yet sure of the effects that exposure to cellphones may have on the brain, but it is probably not a good idea for children to be using cellphones a lot. Rather be safe than sorry and restrict their talk time to a minimum.
Brain under construction
From chaotic connections between neurons to the most intricate network of pathways in a few spurts of mind-blowing growth
Frontal lobe areas, where we interpret our feelings, start developing relatively late and mature even later. This explains why young adults are often more emotional and impulsive than older people.
Motor skill development of large muscle groups starts soon after birth. By the age of five a child has enough fine motor skills to start playing the piano.
Children start speaking in their second year when the newly developed speech area in the temporal lobe starts maturing. A growth spurt between the ages of six and 12 in the language areas makes this period critical for learning languages.
A child of six can see an oncoming vehicle but his brain can't judge speed, size or depth yet. This requires very fast processing of complex calculations. Only at age nine can the child's brain process the information for him to cross the street safely
Music and sport can help structure the brain for a child to develop or sharpen his skills. Try to guide them in fascinating directions because teens become more selective about the skills they wish to improve.
The teen and the young adult brain
This is a sensitive time when feelings become linked to rational thought. Just before puberty there is a second wave of overproduction of grey matter: neurons and their branch-like extensions. This surge involves the highest levels of the brain (planning, reasoning, social judgment as well as emotional and impulse control), which are gradually shaped as teenagers mature.
By their teens most young people will know their mental strengths and potential for success in particular areas. They become more selective about the skills they wish to improve and the subjects that interest them most. They acquire strong rote-memory skills and develop different learning techniques for different memory tasks, for example history or literature as opposed to scientific principles.
The adolescent brain is very malleable and your teenager's choices will determine the quality of his brain. There's an overabundance of new connections in the brain, some of which are pruned away, increasing the brain's efficiency. Parents can help shape this pruning.
Music, maths and sport can help structure the brain faster and better than simply hanging out. Insist on two hours "brain work" each evening before allowing your teenager to watch TV or play computer games.
Most teens average seven and a half hours' sleep a night but for brain development nine hours should be the goal. Sleep deprivation causes problems in the development of the frontal cortex which affects learning and memory.
Your teenager becomes amazingly inventive. Older teens investigate new ideas and schemes and plan their future. They also work out key social skills for themselves, for example how to negotiate with others and how to plan and organise their work and social life.
Certain areas of the brain don't mature for many years, which explains why young adults are often more emotional and impulsive than older people. Frontal lobe areas, where rational processing of emotion takes place, develop relatively late.
Consequently teenagers, who are hungry for stimulation, often take risks without fully understanding the consequences.
The frontal lobes, which enable them to curb such behaviour, are among the last areas of the brain to develop fully. Located right behind the forehead, the frontal lobes grow larger than adult size in puberty and are refined only in the early twenties.
This explains why teenagers can rationalise almost as well as adults when all is calm, but not in stressful situations - the frontal lobes cannot cope.
When the penny suddenly drops for a struggling student and the brain makes sense of the subject material it is because the area that helps us to stay focused has matured. The thick bundle of nerve fibres connecting the left and right hemispheres of the brain enlarges. At this point key areas linked to language development and spatial reasoning mature.
Young adults become better at "executive" thinking because there are more mature, efficient connections within the grey matter. The all-important frontal lobes, the site of reasoning, are further refined, along with emotional tone (altruism, love, compassion and insight) and motor skills.
Once they've embarked on their chosen career, young adults have to acquire and remember specialist knowledge and the skills required for their work. How do they do it? Practice, practice, practice.
The ability to learn new information related to their job stimulates the ability to acquire further specialist knowledge. It's a never-ending treadmill! At 30 there's another growth spurt; this is usually when insight makes people realise their parents are smarter than they thought.
The midlife and beyond
About 50 000 neurons die each day in a healthy person. Eventually this adds up to about 10 per cent of the original total. At 75 the physical weight of the brain is about nine tenths of its maximum and blood flow through the brain has reduced by almost one-fifth.
Does the loss of grey matter mean we all become less intelligent as we grow older? Not necessarily - instead of losing our faculties, brain function can even be improved.
The brain is a specialised machine with specific regions handling specific operations. The greatest divergence comes between the left and right hemispheres, which often work almost independently of each other. One hemisphere can be solving an equation while the other tends to basic chores.
As we age the two halves work increasingly in tandem because the walls between the hemispheres seem to fall away. Sometimes the hemispheres are so efficiently integrated that our thought processes are better than before.
When the whole organ works better than the sum of its parts you begin to use the entire body of information in your brain - exactly what wisdom is. Because of their capacity for reflective thinking older adults play particular roles in human culture, as in the case of judges and peacemakers.
The upside of the ageing brain is that it brings new thinking patterns online and cross-indexes existing systems like never before. You manage information much better than when you were younger. Your brain makes leaps it couldn't make as easily before.
The middle-aged brain (35 to 65 and even beyond) is much more elastic and supple than previously thought. Healthy adults have lots of myelin (fatty white sheathing) in the frontal and temporal lobes, where big thoughts live. And guess what: it peaks at around 45 or 50!
There is no known limit to the amount of information you can store or the amount of learning you can enjoy. Any cerebral activity challenges the brain and maintains healthy neural networks. Whenever you learn something new, new branches of nerve fibres and new connections are formed. If you don't stimulate your brain the connections are destroyed. Remember the old saying, "Use it or lose it"!
75 and beyond
Grandpa has become ever so cranky and granny so forgetful! The reason for this is men lose their brain tissue earlier than women and they lose more of it.
This happens mostly in the frontal and temporal lobes, which are concerned with thinking and feeling, and may explain personality changes in older men such as irritability. Women tend to lose brain tissue in the areas where memory and visual-spatial abilities are located, which is why some older women have difficulty remembering things and finding their way about.
Some older people have trouble with memory tasks either because their memory skills have become rusty or because they never learnt any in the first place.
What can go wrong?
Dementia is a condition resulting from disease in the brain and involves the decline of normal brain functions, memory loss, confusion and personality changes. It affects about one in 100 people aged between 65 and 70 and one in 20 aged between 70 and 80. For the very elderly - people over 80 - figures are uncertain.
It's the most common cause of dementia (diagnosed in 80 per cent of cases). The first symptoms are poor shortterm memory, followed by an inability to concentrate as well as personality changes. Mental activity such as reading, writing and attending adult education classes can help maintain thinking abilities.
The brain has the power to mend damage caused by a stroke. Nerve cells affected by the stroke usually die, but connections between surviving cells can regrow and bypass damaged areas. The brain can resculpt itself and often regains some of the functions lost immediately after a stroke.
(This article first appeared in YOU Pulse; Summer, December 2007.)
Learn more about brain development on Parenting24.