Progress in Physiological Psychology, Volume 2 is a five-chapter text that covers the advances both in experimental and theoretical studies on physiological psychology. Chapter 1 deals with the application of recording of cortical steady potentials (DC potentials) to problems of motivation and learning, reflecting electrical changes correlated with these aspects of behavior and suggesting that steady potential shift may be a neurophysiological manifestation of Hull's behavioral concept of reaction potential. Chapter 2 provides an overview of the neurological mechanisms at work in learning and memory, especially the electrophysiological and neurochemical processes. Chapter 3 considers first the general properties of populations and communities of plants and animals, followed by a discussion on the influence of population pressures on various stages of reproductive function. This chapter also surveys the various theories concerned with the integration of mechanisms that regulate population growth and the natural selection of these mechanisms. Chapter 4 discusses the social interactions and population pressures, which act through the neuroendocrine systems to produce the degenerative changes that characterize arteriosclerosis, pancreatitis, cancer, and other diseases so prominent in civilized man. Chapter 5 describes the maternal and mating behavior showing the important role of limbic structures in positive as well as in negative motivated behavior. This book is directed toward neurophysiologists, psychologists, and researchers.