When do synapses stop forming

On the receiving post-synaptic side, special receptors for neurotransmitters change the chemical signal into an electrical signal, repeating the process in this next neuron in the chain. The number of synapses in the cerebral cortex peaks within the first few years of life, but then declines by about one third between early childhood and adolescence.

How does nutrition affect the developing brain? Are there critical periods in the development of every brain function? What is a "Critical Period" in Brain Development?

Skip to main content Skip to footer. Close Search Submit. Upcoming Events. Learning Center. Search Submit. Resource When is the brain fully developed? New connections are continually created while synapses that are no longer in use degenerate. To date, little is known about the mechanisms behind these processes. Markus Butz has now been able to ascribe the formation of new neural networks in the visual cortex to a simple homeostatic rule that is also the basis of many other self-regulating processes in nature.

With this explanation, he and his colleague Dr. Arjen van Ooyen from Amsterdam also provide a new theory on the plasticity of the brain -- and a novel approach to understanding learning processes and treating brain injuries and diseases. The brains of adult humans are by no means hard wired.

Scientists have repeatedly established this fact over the last few years using different imaging techniques. This so-called neuroplasticity not only plays a key role in learning processes, it also enables the brain to recover from injuries and compensate for the loss of functions.

Researchers only recently found out that even in the adult brain, not only do existing synapses adapt to new circumstances, but new connections are constantly formed and reorganized. However, it was not yet known how these natural rearrangement processes are controlled in the brain. In the open-access journal PLOS Computational Biology , Butz and van Ooyen now present a simple rule that explains how these new networks of neurons are formed.

Following the amputation of extremities, brain injury, the onset of neurodegenerative diseases, and strokes, huge numbers of new synapses are formed in order to adapt the brain to the lasting changes in the patterns of incoming stimuli. These results show that the formation of new synapses is driven by the tendency of neurons to maintain a 'pre-set' electrical activity level.

If the average electric activity falls below a certain threshold, the neurons begin to actively build new contact points. These are the basis for new synapses that deliver additional input -- the neuron firing rate increases.

This also works the other way round: as soon as the activity level exceeds an upper limit, the number of synaptic connections is reduced to prevent any overexcitation -- the neuron firing rate falls.

Similar forms of homeostasis frequently occur in nature, for example in the regulation of body temperature and blood sugar levels. However, Markus Butz stresses that this does not work without a certain minimal excitation of the neurons: "A neuron that no longer receives any stimuli loses even more synapses and will die off after some time.

Synaptic pruning is a natural process that occurs in the brain between early childhood and adulthood. During synaptic pruning, the brain eliminates extra synapses. Synapses are brain structures that allows the neurons to transmit an electrical or chemical signal to another neuron.

As more is learned about synaptic pruning, many researchers are also wondering if there is a link between synaptic pruning and the onset of certain disorders, including schizophrenia and autism. During infancy, the brain experiences a large amount of growth. There is an explosion of synapse formation between neurons during early brain development. This is called synaptogenesis. This rapid period of synaptogenesis plays a vital role in learning, memory formation, and adaptation early in life.

At about 2 to 3 years of age, the number of synapses hits a peak level. But then shortly after this period of synaptic growth, the brain starts to remove synapses that it no longer needs. Once the brain forms a synapse, it can either be strengthened or weakened. This depends on how often the synapse is used. The process of removing the irrelevant synapses during this time is referred to as synaptic pruning.

Early synaptic pruning is mostly influenced by our genes. In other words, whether or not a synapse is pruned is influenced by the experiences a developing child has with the world around them. Constant stimulation causes synapses to grow and become permanent. But if a child receives little stimulation the brain will keep fewer of those connections.

The timing of synaptic pruning varies by brain region. Some synaptic pruning begins very early in development, but the most rapid pruning happens between roughly age 2 and Brain development in the embryo starts just a few weeks after conception. By the seventh month of a pregnancy, the fetus starts to emit its own brain waves.

New neurons and synapses are formed by the brain at an extremely high rate during this time. During the first year of life, the number of synapses in the brain of an infant grows more than tenfold. By age 2 or 3, an infant has about 15, synapses per neuron. In the visual cortex of the brain the part responsible for vision , synapse production hits its peak at about 8 months of age.

In the prefrontal cortex, peak levels of synapses occur sometime during the first year of life.