The second edition of the book "Neuroplasticity and its Dark Sides" stresses some less well-known aspects of neuroplasticity, namely that there are two kinds of neuroplasticity, one that is beneficial to a person and one that may be harmful. It also discusses that there are functions that can easily be changed through activation of neuroplasticity while other functions are more difficult to change or more or less "hard-wired." Activation of neuroplasticity is essential for learning new skills and adapting to changing demands, but neuroplasticity can also create symptoms and signs of common and widespread diseases such as chronic neuropathic pain and severe tinnitus. Such maladaptive neuroplasticity is also the primary cause of other plasticity disorders such as spasticity, and it may be involved, together with other factors such as the immune system, in the development of diseases such as fibromyalgia, the chronic fatigue syndrome and probably many other disorders. Understanding these dark sides of neuroplasticity is vital for treatment of many common diseases. Reversing such bad plastic changes would be an ideal treatment of many disorders if it could be done efficiently and with little adverse side effects. Another less well-understood property of neuroplasticity, namely that not all brain systems are plastic is also discussed in the book. The fact that attempts to change sexual preferences have been unsuccessful indicates that there are functions of some neural circuits that cannot be changed or are difficult to change. This means that there are neural circuits that are not plastic, but "hard-wired." Long-term memory and a person's personality are other examples of common functions that are stable during a person's life indicating that some very complex circuitry in the brain may be less plastic than earlier assumed. The failed success in the treatment of posttraumatic stress syndrome (PTSD) is another example of functions that are difficult to change. The book provides a comprehensive description of the basis for neuroplasticity in general. The ability to change the efficacy of synapses and the change in protein synthesis are discussed in detail. The role of "maladaptive plasticity" in the development of many disorders of the nervous system and how the understanding of neuroplasticity can benefit diagnosis and treatment of many diseases of the nervous system are other themes of the book.