It’s three weeks since you were conceived, and your brain has just started to form. A quarter of a million neurons are growing in your head with every single minute that passes.

Under the guidance of your genes, you are now forming the brain cells that you will think with all your life, along with cells in your ears and eyes. But your brain will really get busy from the age of twenty weeks until you’re born. It’s building structures and circuits that will lead to the adult you will become.

Brain-building
In your developing brain, cells migrate outwards to form six layers in the neocortex, part of the folded outer layer of your brain responsible for learning and memory.

Experts used to think migrations stopped at birth. But new research shows that some neurons carry on migrating up to three months after you’re born, triggered by interactions with your environment. We know of no other mammal that does this – and it is an example of the way in which your brain is shaped by experience.

Brain diversity
Every human brain has the same structure. You think primarily with the cerebral hemispheres, the two wrinkled masses that look like walnut halves. Incorporated between them is the limbic system that processes emotion, and beneath is the cerebellum, associated with movement.

The brain stem, consisting of the midbrain, pons and medulla, handles life support. But your personality and character result from the particular way in which your brain is wired up.

You are now in your childhood, and your brain is making up to 1,000 new connections every second. Each neuron is busy sending out extensions called axons that transmit information, and dendrites that take in information.

As a result, each neuron in your neocortex ends up with about 15,000 connections, called synapses, by the time you are three years old. You’ll go on learning new things and gaining experience all your life, strengthening useful connections all the time.

How do you learn?
All your thoughts, actions and emotions involve a living network of brain cells and chemicals.

Neurons pass on information using electrical impulses that release chemicals called neurotransmitters at the synapses. When the chemical signal is strong enough, the next neuron is triggered and transmits the signal.

This communication is the basis of circuits within and between brain regions that enable you to learn language, recognise patterns and instruct your body to carry out intricate tasks.

Word Detective
Psychologists and neuroscientists at the University of Oxford are working together to research how children’s brains recognise and process words.

By studying how the brain responds to different types of words during a variety of reading tasks we are beginning to understand the complex neural circuits that serve our ability to read.

The Word Detective game below is based on a lexical decision task used by scientists in this research.

In the Word Detective above some made-up words sound like familiar words - such as ‘brane’ and ‘brain’. When asked to sort real from fake words in this type of lexical decision task, people are generally slower to reject familiar-sounding fake words than those which don’t sound real.

This tells us that as we read, visual word forms activate speech areas in the brain, and this feeds into our decision-making when deciding if a word is actually real or not.

You have now reached your teenage years. How do you feel? Your brain is at peak performance. Its capacity to think now matches an adult’s, and its ability to learn will never be greater.

During this vital period, your prefrontal cortex, an area at the front of the brain responsible for planning and decision making, is undergoing a pruning process in which active connections are strengthened while others are lost.

It’s good news for your ability to explore and learn, but means you are not yet able to take rational control of your limbic system, which handles your emotional responses.

During adolescence it can be hard to read emotions and social situations because the brain’s connections between areas like the amygdala, in the limbic system, and control regions of the brain are still developing.

Teenagers’ initial reactions to social scenarios are often emotional, but an Oxford study showed that by asking adolescents to re-evaluate a social scene, their brains’ control circuits came into play, allowing for a more rational assessment and interpretation.

This kind of re-evaluation is an important tool in helping adolescents cope with anxiety.

Brain pruning
Your brain won’t be fully developed until you are in your mid-twenties – much later than experts once thought.

It’s busy throughout adolescence completing a huge housekeeping project that started in your childhood. The number of connections between brain cells drops by half as the brain clears away unused pathways.

The remaining connectors develop a wrapping called myelin that increases the speed at which they can send signals. This fatty white substance gives them the pale appearance of the brain’s white matter.

Night owls
Sleep is critically important to good health and a positive mood. But between the ages of ten and 21, changes in the brain can get your sleep patterns in a mess.

Experts don’t know exactly why, but the internal clock that controls sleepiness runs up to three hours late at this time of life. What’s worse is that you probably need nine hours of sleep, instead of an adult’s eight.

Some schools have decided to try starting the school day later to see if it improves students’ alertness, memory and learning.

Now that you’ve reached 25, the pieces of your brain’s complex puzzle have fallen into place. From the visual area at the back of your brain, to the prefrontal cortex handling control and planning, all the functional areas are mature.

Some days you may feel more on-the-ball than others. However, it’s a myth that you use only ten percent of your brain capacity. Scans show your entire brain functioning even while a specific part is particularly active. And new research is revealing much more detail about which areas do what.

Making sense
Your senses have been fully functional since you were young. They use an army of detectors in your eyes, ears, nose, tongue and skin to gather signals from the world around you.

Each part of your retina, the light-sensitive layer at the back of your eye, links to a location in your visual cortex. Signals travel along neural pathways, creating a representation of what you see. In a similar way, your entire skin surface maps to areas of your thalamus and parietal lobes so that you can tell where and how a sensation originated.

But new research is revealing a surprising crossover between many senses that is still under investigation.

Busy being happy
Your brain has several chemical routes to making you feel happy. The neurotransmitters dopamine, serotonin, oxytocin and endorphins can all be released by good experiences.

However, a win or achievement may not result in the happiness you might expect. Dopamine neurons fire at the anticipation of reward but then reset. It’s as if your brain is tuned to anticipate reward rather than enjoy receiving it – part of its ongoing mystery.

At the ripe old age you’ve now reached, your brain has been hard at work for decades. Ever since you were forty, your brain has been shrinking by five percent per decade. Levels of the neurotransmitter dopamine that sends signals around the brain have also been dropping, a normal part of ageing.

But there continues to be remarkable power in your brain. Neurons are still building new connections and circuits, preserving your ability to adapt and learn. This property, called plasticity, seems to be best maintained by exercise.

Keeping it fresh
New neurons are born even in the ageing brain – but only in two areas, as far as we know. They occur in the forebrain where they move to the area associated with smell. The other place is in the hippocampus where they may have a role in the formation of new memories.

Whether the cells flourish and integrate into their new brain areas does seem to be influenced by genes. However, there is also evidence that mice which exercise and have new experiences see fewer brain cells dying off.

Memory switch
You might be worried about losing memory in old age. Some memory function decreases from middle age onwards, particularly memories of episodes in our lives. However, your memory for facts and meanings increases during adulthood until eventually declining when you are very old.

Scientists are studying memory with a technique called optogenetics. They use genetic modification to make particular
brain cells in mice into light-sensitive switches. Then they can switch the cells on and off using light, helping reveal how memories are stored, could be wiped, or possibly restored.