[Neuroplasticity: synaptogenesis during normal development and its implication in intellectual disability]

Neuroplasticity is the biological capacity of the nervous system to modify its structure and functioning to adapt to both physiological and pathological variations in the environment. Its main physiological consequences are learning and memory, and its pathological outcome is neurological rehabilitation. The continuous change and initial fragility of the developing brain make the embryonic and foetal periods especially plastic (what is known as developmental neuroplasticity). The progressive reduction in plasticity, however, is never complete and the capacity to modify the brain circuits in response to new learning (adaptive neuroplasticity) or brain injuries (reactive neuroplasticity) remains throughout the individual's entire lifespan. The main neurobiological mechanism underlying neuroplasticity is the formation of synaptic contacts between neurons. Neurodevelopmental disorders are associated to functional anomalies of the brain, often derived from the lack of adaptive or reactive capacity of the brain to modify circuits that are malformed or damaged by genetic or environmental anomalies. They are traditionally associated with the appearance of intellectual disability and mental illnesses. This review deals with the development of the neuroplasticity of the brain and its neurobiological mechanisms. Some of the cellular and molecular processes involved in its normal development are also examined, together with the possible consequences deriving from alterations affecting them.