As often used in relation to the central nervous system (CNS), the term plasticity refers to the malleability of neuronal connections. The degree to which the nervous system shows plasticity has been one of the seminal questions that has driven man’s curiosity about the brain. On the one hand, it is clear that the CNS pathways in mammals do not fully recover from injury, suggesting that, once formed, the brain and spinal cord must be structurally inert. Yet it is obvious that our physical and mental abilities can change and that, at least to some degree, we can regulate these phenomena in relation to environmental conditions.