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Brain maturation takes much longer than anticipated
Last reviewed: 30.06.2025
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The reduction in the number of synapses in the cerebral cortex in the late stages of its development continues until almost thirty years of age.
In the formation of the human brain, a major role is played by the reduction in the number of synapses, no matter how paradoxical it may sound. This fact has long been known to scientists: during intrauterine development and throughout childhood, more and more new synapses are formed in the brain, and then their number begins to rapidly decrease. It is due to this reduction that a person is believed to have the opportunity to learn and master new skills.
Overproduction of synaptic connections in childhood is necessary to give the brain something to choose from, but later, the excess of electrochemical connections between neurons can confuse and slow down the gray matter. Maintaining synaptic connections is costly, so the brain gets rid of unnecessary ones to direct more resources to important neural circuits; in other words, less is more. Brain maturation can be compared to gardening - when trees and bushes are trimmed of unnecessary branches to make the crown more lush.
It was generally accepted that the brain reaches the necessary "synaptic equilibrium" by the age of 20. But it turned out that this age is greatly underestimated. A group of neurophysiologists from the universities of Zagreb (Croatia) and Yale (USA) studied the structure of the prefrontal cortex in 32 people, whose ages ranged from one week to 91 years. The scientists were interested in the density of the so-called dendritic spines of the cortex neurons - various membrane protrusions on the surface of neuronal processes. The spines, roughly speaking, represent a connector for connecting with another neuron; synapses are formed precisely with the help of such membrane protrusions.
As expected, the density of dendritic spines on cortical neurons increased until age 9, after which the membrane projections began to retract, but this retraction did not end with the exit from adolescence, but continued almost until age 30. The scientists presented their results in the journal PNAS.
It turns out that the brain improves its architecture much longer than expected. Therefore, on the one hand, you can study a lot after twenty years, but with the fear that the brain is already tuned to other things and will give in to something new. On the other hand, according to the researchers, the results allow us to re-evaluate the causes and development of some mental illnesses. For example, there are different opinions about schizophrenia, whether it occurs as a result of developmental problems or due to some degenerative processes occurring in the already formed brain. Probably, at least some cases of schizophrenia can be attributed to the first option...
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