Psychology is the scientific study of human and animal behaviour with the object of understanding why living beings behave as they do. As almost any science, its discoveries have practical applications. As it is a rather new science, applications are sometimes confused with the science itself. It is easier to distinguish what is 'pure' and 'applied' in older disciplines: everybody can separate physics and mathematics from engineering, or anatomy and physiology from medicine. People often confound psychology with psychiatry, which is a branch of medicine dedicated to the cure of mental disorders. Some topics that 'pure' psychologists may study are: how behaviour changes with development, when behaviour is instinctive or learned, how persons differ, and how people get into trouble. 'Applied' psychologists may use scientific knowledge to find better ways to deal with adolescents, to teach, to match persons with jobs, and to get people out of their troubles. Accordingly, several branches exist of psychology: developmental psychology, animal psychology, educational psychology, psychotherapy, industrial psychology, psychology of personality, social psychology, are but some of them. Physiological psychology is a field akin to neurophysiology that studies the relation between behaviour and body systems like the nervous system and the endocrine system. It studies which brain regions are involved in psychic functions like memory, and activities like learning. It also studies the complex interaction between brain and hormones that gives rise to emotions. .
Animal behaviour is studied by psychologists mainly in laboratory. The study of animal behaviour in their natural habitats is undertaken by the science of ethology. The comparative study of human and animal behaviour is one of the sources of evolutionary psychology that tries to understand how evolution has shaped the way we think and feel. Educational psychology concentrates on those aspects of the psychic activity that have to do with learning.