We might believe that the adolescent brain is unbalanced, with an overactive reward system that leads to impulsive decision-making. Indeed, it undergoes numerous structural and functional changes, which contribute to late cognitive and emotional maturation. But most other animals leave the nest at the end of puberty and do not experience this “prolonged” adolescence… What selective advantages lie behind the duration of this brain development?
As animals transition into adulthood and independence, they must learn new skills, leave their birthplace, and experience new environments. During these uncertain times, it has been shown that animals that explore new solutions are more likely to pass on their genes to the next generation. This is what inspired researchers at the University of California at Berkeley in 2022: they subjected 291 volunteers, aged 8 to 30, to various cognitive experiments. “ Adolescents do better than adults in conditions that are more uncertain or random » says Linda Wilbrecht, who led the study. The conclusions are similar to those from the observation of other speciesspeciesand in particular primates: in random circumstances, adolescents are apparently more willing to try new solutions, which provides them with information to best adapt their way of acting in the future.
Trial, success and reward
These results would be linked to greater activity in the reward centers of the brain, previously considered dysfunctional in adolescents. They send a signal to the cerebral cortex, to allow it to adjust neuronal communication pathways, and thus optimize behavior. Linda Wilbrecht explains: “ The adolescent brain is designed to explore, discover and connect (…) literally, because neurons extend and form new connections. And we need to experiment first so the brain knows which connections to keep “. This exploratory behavior would therefore be the result of an evolution common to other species. However, in most of these same species, adolescence is limited to puberty, while in humans or certain primates, it extends well beyond… Why such a specific evolution?
Why this delayed dynamic?
From childhood to adolescence, the brain undergoes a remarkable process called “synaptic pruning”: it eliminates unnecessary neuronal connections, guided by genetic factors and environmental influences, in order to refine cognitive processes and improve brain function. . Thus, the brain becomes more specialized and more efficient.
During adolescence, two brain regions will develop according to this principle, but in a desynchronized manner. While the ventral striatum and limbic systemlimbic systemincluding the amygdala – linked to reward – are functional around the age of 15, the prefrontal cortexprefrontal cortex, is only mature around the age of 25. What does this mean in practice? First, the early development of reward-related brain systems leads to an increased manifestation of thrill-seeking and novel experiences. Associated with dopamine,hormonehormone pleasure and reward, and social and environmental factors, adolescents are impulsive, sensitive and empathetic. This behavior will come into balance with the maturation, although later, of the prefrontal cortex. Also called the executive center, it acts on the control of higher order executive functions: impulse control, decision-making and long-term planning capacity, development of social interactions… It experiences a real optimization of its performance: synaptic pruning and myelination of axonsaxons which accelerates the speedspeed transmission of thenerve impulsesnerve impulses, all under hormonal influence – the activation of the hypothalamic-pituitary-gonadal axis does not only act on the production of sexual hormones. Adolescence is therefore not limited to pubertypubertyand cognitive and emotional maturation continues well beyond.
Brain construction, social construction
Structural and functional changes in the cortex are associated with the development of cognitioncognition social, guided by experiences and interactions. These same social situations also activate the neural networkneural network of the ventral striatum, this same network developed earlier in adolescents. It is therefore very likely that the developing brain is much more capable of adaptation in mattermatter of social relations than what is admitted. The construction of self-esteem and one’s choices being influenced by a desire for conformity and belonging to a group, the adolescent must find a balance between this individual-society duality, hence the importance of a stable and stimulating environment at the same time.
Although the existence of biological bases linked to the phenomena of adolescence is established, in particular thanks to progress in brain imaging, their precise role remains to be defined, and this period of life cannot be reduced to somatic transformations. puberty, nor to a psychosocial construction. The proof, when we discover that what seems to be a structural imbalance is perhaps a selective advantage hiding hitherto underestimated capacities for adaptation and socialization.
