Psychopathology, the science of mental dysfunctions, can and should be based on (cognitive) neuroscience.In particular, concepts such as neuronal activation, neuroplasticity, and neuronal death can be used to understand, and to treat, mental dysfunctions. Some of the basic principles are illustrated using recent examples, such as the plasticity of the serotonin system of the crab caused by a single social interaction, the 'psychotherapy' of specific language impairment and the effects of stress on the hippocampus in human beings.