This book brings together a variety of topics that are dispersed throughout the literature: correlations among neurones, synaptic plasticity together with brain theories based on these mechanisms, motor systems at the spinal cord level, and related hypotheses. Its main thrust is to outline common working principles of neural assemblies and to develop a novel concept of spinal motor systems that should stimulate new ideas and experimental research. In addition to a review of the state of affairs in various fields, this book supplies a unified approach towards understanding the nervous system.