At the turn of the 21st century, the development of laser scanning microscopy combined with the methods of neuronal transfection with fluorescent proteins permitted the first ever real-time visualization of excitatory synapses following the induction of learning- related patterns of activity in living neurons in vitro, and later following sensory experience in living animals. These techniques, that are still improving today, led to the discovery of a causal link between learning and memory and structural plasticity of synapses, leading to long-term neuronal network remodeling. It has opened a new era in the study of the mechanisms that underlie learning and memory, and provided new therapeutic leads for brain disorders. This thesis describes my scientific contribution in this context.