The mammalian nervous system is generated by complex genetic and epigenetic programmes that warrant the structure to be defined already at birth. This structure allows appropriate behavioural responses in order to guarantee survival and development. However, sensitive, motor, sensoriale and cognitive stimuli, through the interaction with the environment, play a role for defining the neural "circuits" after birth. These changes occur, according to what is known from decades, at synaptic level and imply a modification of the "strength" of the synaptic connection itself as a response to an internal/external trigger. In the last decade, a great deal of data has provided the evidence that the changes of the nervous tissue could also be structural in nature. It is well known, in fact, that new synapses may arise, other are eliminated, through a remodelling of nervous cells branching. Moreover, new cells and neurons may form. Altogether, these modifications are generically called plasticity, and include biochemical and structural modifications, and neurogenesis. Genetic, pharmacological and environmental factors may modulate this plasticity, through continuous updated cultural advances. The knowledge and the eventual exploitation of these mechanisms represent a clinical opportunity in the field of pharmacology, genetics, and motor and cognitive rehabilitation. A key point is represented by the recently- acquired concept that plasticity regards the entire individual lifespan, mainly during childhood but also up to some aspect of elderly. Environmental stimuli reach the cerebral structures via the sensory organs, that thus represent an ineludible tool to mediate sensations, perceptions, memory, speech, the cognitive and affective experiences that are expression of the brain function and, at the same time, nourish plasticity. It is the aim of the present PhD to study this phenomenon in depth in its different manifestations that are displayed in the neurological and psychiatric clinical practice, as well as in the various district of the Sensory Organs.