Which part of the brain finishes developing between the ages of 20 and 25?

Key points about adolescent brain development

• a safe environment where teenagers have consistent loving support is vital for the brain to develop well
• adults who talk to children as they are growing up really help
• when you are talking to teenagers be careful to check what emotion they are seeing in you, and make sure you always acknowledge their emotions first and then help them to be able to think about what they are feeling
• young people need adults to believe in them and encourage them
• teenagers respond better to rewards than to punishment
• they need clear, consistent boundaries, and very importantly, their growing capacity and ability to do things independently needs to be respected

When does brain development happen?

The brain develops very rapidly in the first 3 to 5 years of life, and all the structure and building blocks are present by the age of 9. The different centres of the brain develop and become functionally connected over time. The last part to mature is the prefrontal lobe. This happens during adolescence. Many things affect brain development including genetics, individual and environmental factors.  

Why does the brain take so long to develop?

Human beings are the only animals that are born completely helpless, and we have the biggest size of adult brain. If we were born with an adult-sized brain our heads would not fit through our mothers' hips. Brain development that continues after birth also helps us better adapt to our living environment and increases our chance of survival.

We used to think that once children had gone through puberty and growth had finished, development was complete. Then MRI scanners were invented and they showed that the brain goes on changing for a long time after puberty has finished, and may not be complete until nearly 30 years of age.

The following image shows that the brain doesn't change much in size between 5 and 20 years of age. What changes is the colour. The blue colour shows all the connections happening between all the parts of the brain that are already formed.

How does the brain develop?

Some people like to think of the brain in 4 parts.

1. The spinal cord and the base of the brain

Delivers messages to and from all parts of the body and controls what happens in the parts you don't have to consciously think about like the heart, lungs and digestion.

2. The cerebellum

Controls and coordinates movement and other brain processes.

3. The amygdala and hippocampus

Control emotion and memory.

4. The cortex

Connects up all the senses and thinking part, including the prefrontal cortex which is involved in fine judgement and control.

Brain development

The brain is thought to develop and connect functionally in stages. The emotional areas of the brain (the limbic system) are present at birth, but regulation of emotions moves from being more of a shared responsibility (with parents) in childhood, to an individual responsibility in adolescence. This process requires new connections to be formed between the cortical or higher level thinking and the emotional areas of the brain. It also leads to adult level decision making, planning and thinking.

Which part of their brain do teenagers use most of the time?

Teens often 'think with their feelings'

Experiments have been done to show that teens often 'think with their feelings'. Scans of the brain can be done to show different parts lighting up when they are being used. When adults and teens look at faces showing different emotions, the part of their brains that light up are different. Adults use their prefrontal cortex to look at faces and try to decide what emotion is happening. Teenagers use their amygdala rather than their prefrontal cortex most of the time. In other words, they are using their emotions to try and understand emotion.

It helps if adults can understand how this feels for teens

To understand how this feels, imagine you have lost your keys and you are already late for work. Think about how many times you look for the keys in the same place - 5, 10 even 20 times. You panic - you no longer think with your cortex, you are thinking with your emotions. Remember how it feels if someone tells you to calm down and think sensibly about when you last had them. That is how your teenager feels when they are running on their emotions because their brain hasn't developed that linkage.

When talking to teens, be careful to check what emotion they are seeing in you

Often teens can misinterpret emotions and they see anger when in reality you are feeling anxious. This can often lead to many moments of miscommunication. So, when you are talking to teenagers be careful to check what emotion they are seeing in you, and make sure you always acknowledge their emotions first and then help them to be able to think about what they are feeling. 

What can help brain development?

Talking to your teen really helps

Adults who talk to children as they are growing up really help. A safe environment where they have consistent, loving support is vital for the brain to develop well. Young people need adults to believe in them and encourage them. Teenagers respond better to rewards than to punishment. They need clear, consistent boundaries, and very importantly, their growing capacity and ability to do things independently needs to be respected.

Teens need opportunities to grow many different skills

As their brain grows and gets connected functionally, they need to learn that they don't have to be dependent on their parents but can become interdependent with other adults as they mature. They need opportunities to grow many different skills and to contribute those skills in a way that is valued. The brain develops in a way that produces lots of connections that are then removed if they are not used. So take care to encourage lots of connections to be used.

Develop good habits around activities like thinking positively, eating and exercise during the teen years

Another principle is that when connections 'fire together they wire together', so this is a vital time to develop good habits around activities like thinking positively, eating and exercise as that wires together for adulthood. We know that the brain can change throughout life but it is much easier to get the 'wiring right at the start, in teenage times'. It takes a lot of hard work to rewire as adults.

What harms the development of the brain?

Abuse (verbal, emotional, physical, sexual or neglect)

It is now well established that if children experience any sort of abuse (verbal, emotional, physical, sexual or neglect), especially in the early years of life, it can affect how the brain is wired and functions. Sometimes this is hard to change, so it is very important to protect children throughout their development. This is especially important at times of peak brain development during pregnancy and the first 5 years of life and during the second phase of brain development around puberty.

Alcohol and drugs

Read and watch videos about adolescent brain development and the effect of alcohol and drugs on the developing teenage brain.

Find out about teens, drugs and the developing brain

Read about alcohol and young people

See more KidsHealth content on parenting teens

Check out KidsHealth's section on parenting teens