How Does Synaptic Pruning Affect Learning?
Pruning is a mysterious brain process. From birth to childhood, the number of brain connections skyrockets; but after adolescence, they dramatically decrease.
This reduction in density is a result of the brain’s plasticity, which enables it to eliminate unneeded synapses. Just like pruning a rosebush, this elimination focuses resources on the stronger, more useful neural circuits.
How It Works
As you learn, your brain’s connections grow and strengthen. However, weak or unnecessary connections are “pruned” away as your brain assesses and discards ineffective ones. This pruning process is also called neuroplasticity.
During the day, you are constantly receiving stimuli that can overstimulate your brain cells and prevent them from properly assessing and retaining new information. That’s why sleep is the best time for your brain to prune connections, as it’s less preoccupied with sensory input.
Scientists have found that certain proteins in your brain can increase or decrease the amount of neural pruning that occurs. These proteins are similar to those involved in the immune system and can help shape your neural network in ways that optimize memory and learning.
Why It’s Important
Brain connections called synapses bloom like trees during infancy. The victorious ones survive; unsuccessful ones fade away in a process of apoptosis, or cell death. This sifting of connections is called neural pruning and occurs in different parts of the brain at different times.
Researchers have now shed light on a nuanced protection/punishment system that governs synaptic pruning. By studying mouse mitral cells, a neuron type in the olfactory system, they found that neurons receiving a specific neurotransmitter signal are protected through a series of chemical pathways while other dendrites within the same cell are triggered to undergo pruning.
This process of clearing out unnecessary synapses is crucial for learning. It makes room for new, relevant connections that can be formed as a result of the day’s experiences. But if it goes too far, or is not regulated properly, it can lead to mental illness. Studies are beginning to suggest that some psychiatric conditions, such as schizophrenia and autism, are associated with glitches in this pruning mechanism.
How It Affects Learning
Scientists think that the pruning of unnecessary brain connections is important for learning and memory. They have shown that mice with a deletion of GABA receptors involved in synaptic pruning are unable to learn spatial locations. This suggests that reversing the process of pruning could help people with autism or schizophrenia who have an over abundance of brain connections.
During an embryo’s early development, new neurons and synapses form at a tremendous rate. By the time a person is 2 years old they have far more connections than they will ever functionally need. Experiences strengthen and retain the connections that prove to be useful, while weaker ones are pruned away.
Pruning is at its peak between the ages of 2 and 10, and slows down as you enter adolescence. It may also occur during sleep, when the brain is less preoccupied by external stimuli. The process is called neural plasticity. It makes the brain more efficient and allows for quick adaptation to new situations.
How It Affects Memory
Once you’ve mastered a skill, you may find that the brain connections that helped you do it decrease in number. This is synaptic pruning, which gets rid of unnecessary or weak connections to free up space for more important ones. The process can be disrupted by neurological disorders, such as autism spectrum disorder and schizophrenia.
In studies of mice, researchers have found that a protein called inhibitory GABA receptors trigger pruning. The researchers also injected the mice with a chemical that reduces GABA activity, which causes pruning to be delayed or abolished altogether.
Neuroscientists have found that newborn neurons migrate along chemically defined pathways, competing to connect with predetermined targets. Those that make it are strengthened and reorganized. Those that don’t are eliminated by a process similar to pruning a bush, making the remaining connections stronger. This remodels the brain, enhancing its ability to learn and adapt. It’s one of the fundamental principles that defines neuroplasticity.