This book collects a set of lectures delivered by in 1964 by the British neurologist John Young. As he put it, "the most important thing of living beings is that they remain alive". A stable state (homeostasis) is what they aim for. Young claims that homeostasis is precisely the job of the brain, the most delicate job of all. Homeostasis requires appropriate responses to the environment, responses whose goal is to keep the state stable. The brain's job is to maintain homeostasis through the selection of appropriate responses. The brain is the computer of a homeostat. This computer uses a memory, or, better, two memories: one memory is the one created by evolution and inherited at birth, that contains knowledge that can be used in many commonly-occurring situations, while the other memory (the one we call "memory", the neural memory) is the one that contains up-to-date knowledge about the outcome of actions during our lifetime.
Young argues that "learning" involves limiting the available choices for action.
Young relates brain research that he conducted on the octupus.