The development of strategies capable to promote nervous system plasticity in adulthood is nowadays an important aim in neuroscience to improve not only cognitive abilities but also to ameliorate pathological dysfunctions. Several studies have demonstrated that adult neurogenesis is regulated by many physiological and pathological stimuli at almost every stage, from proliferation of neuronal precursors until integration and activation of newly formed neurons in the preexisting network. We review the process of generating functional neurons from precursors in the adult brain and its implications in intellectual disability disorders.