Synaptic Pruning

What Is Synaptic Pruning?

Synaptic pruning is a process where your brain removes weak or unused connections between cells, called synapses. This follows a “use it or lose it” rule. Pathways (connections) your brain uses a lot get stronger, while those that aren’t used fade away.

Pruning is an important part of development for everyone. Researchers are still studying whether these changes play a role in mental health conditions like schizophrenia and some neurodevelopmental conditions like autism.

Why does synaptic pruning happen?

This process is an important part of your development. It helps your brain grow and work better by:

• Allowing your brain to focus more energy on the most used connections
• Getting rid of extra pathways so the important ones work better
• Helping your brain adapt to your experiences and environment
• Improving learning and memory
• Supporting clear thinking and sensory processing

When does it occur?

Synaptic pruning happens throughout early development — from infancy through your teen years. In infancy and early childhood, your brain makes a lot of new connections. It then removes those that aren’t used. The number of synapses increases significantly from birth to your first or second year of life. Then, there’s a steep drop during adolescence, and it levels out in adulthood. There is a slight decline after age 65.

How does synaptic pruning work?

It works a lot like trimming a rose bush. By cutting away extra stems and leaves, the plant grows stronger. Your brain does something similar. Here’s how it works:

1. Your brain makes extra connections. Early in life, your brain creates more pathways between brain cells than it will need later.
2. Used connections grow stronger. When you learn, practice skills or repeat experiences, certain pathways “fire up.” Your brain strengthens those pathways because you’re using them a lot.
3. Unused connections grow weaker. Pathways that aren’t used don’t stay as strong as active ones.
4. Weak connections are marked for removal. Your brain sends signals that flag weaker pathways as no longer needed.
5. Unused connections are removed. Special immune-like cells called microglia help clear away marked ones.
6. Your remaining connections work better. With fewer pathways, your brain becomes more efficient, organized and faster at processing information.

What are examples of synaptic pruning?

Here are some everyday examples of how synaptic pruning can show up:

• More organized sight: As visual connections are fine-tuned, children may become better at focusing, reading and making sense of busy or crowded spaces.
• Improved decision-making: During adolescence, your brain continues refining its connections. This can lead to better judgment, improved impulse control and a growing ability to think ahead, even though these skills are still forming.
• Better emotional control and behavior: As circuits mature, children and teens may handle emotions better, act less impulsively and show more predictable behavior.
• More focused interests over time: Young children often enjoy many different activities. As their brain strengthens certain pathways, they often form clearer interests, strengths and preferences.
• Skills fade when they aren’t used: If you don’t practice certain skills, your brain may weaken and remove the connections that support them. This can look like forgetting a language, musical skills or other abilities over time.

What happens without synaptic pruning?

If pruning happens too much, too little or at the wrong time, it could affect how your brain forms and works. This can lead to several problems, like:

• Delayed development: Without pruning, some areas may not fully grow, even into adulthood.
• Trouble processing information: Disorganized circuits overlap, and connections don’t form clear pathways. This can make information processing confusing.
• Difficulty thinking: Extra and weak connections slow your brain down. This makes it harder to strengthen important pathways you use often.

What conditions are synaptic pruning tied to?

Researchers are exploring links between synaptic pruning and certain neurological and developmental conditions. The neurological disorders related to abnormal pruning could be considered “connectopathies,” or diseases of the wiring diagram of the brain. For example:

• Too much pruning: Your brain loses pathways it still needs (may be linked with schizophrenia).
• Too little or delayed pruning: Your brain keeps too many or less-developed connections (may be linked to autism or ADHD).

Some conditions, like intellectual disability or other neurodevelopmental disorders, may fall into either group.

You can’t feel synaptic pruning as it happens. Providers don’t diagnose “pruning problems.” Your provider will instead use evaluations, brain imaging scans and lab tests to diagnose the underlying condition.

What factors influence synaptic pruning?

Several things affect how well synaptic pruning works. These include:

• Sleep: Getting enough sleep each night supports healthy brain development and learning.
• Timing: Pruning happens at specific ages, starting early in life and continuing through your teen years. This timing supports your normal growth.
• Genetic factors: Certain genes, including those linked to your immune system, can affect how much pruning happens and how your brain develops.
• Disease, injury or aging: Pruning may turn on at the wrong time. This may cause you to lose helpful connections later in life instead of during childhood. Some researchers believe that abnormal pruning later in life could contribute to the development of some dementias, like Alzheimer’s disease.